Ellis Whitehouse, a reporter for the Essex Live website, says he worked with Sir David for around five years and that the news is "truly devastating".
"It's a truly horrendous state of affairs and I'm just devastated," he tells the BBC - adding that Sir David was "extremely helpful" to him and his colleagues.
Speaking about the local community, he says: "I imagine this whole thing has been a real shock to everyone."
Everyone "has put their political differences aside and has really come together to support each other", he adds.
BreakingSir David Amess has died
The BBC can now confirm that the man who died this afternoon was Conservative MP Sir David Amess.
The 69-year-old, who is MP for Southend West, was stabbed as he met constituents at Belfairs Methodist Church in Leigh-on-Sea, Essex.
We'll bring you more details as we get them as only limited information has been released at this point.
Police statement in full
Here is Essex Police's statement in full:
"A man has been arrested on suspicion murder after a man was stabbed in Leigh-on-Sea.
"We were called to an address in Eastwood Road North shortly after 12.05pm today (Friday, 15 October).
"We attended and found a man injured.
"He was treated by emergency services but, sadly, died at the scene.
"A 25-year-old man was quickly arrested after officers arrived at the scene on suspicion of murder and a knife was recovered.
"He is currently in custody.
"We are not looking for anyone else in connection with this incident.
"We want to thank the public who alerted us to the incident so quickly.
"We need anyone who saw anything or has CCTV, dash cam or doorbell footage to contact us.
"If you have any information you can submit a report online at https://www.essex.police.uk or use the 'Live Chat' button to speak to an online operator between 7am-11pm.
"Please quote incident 445 of 15 October.
"You can also call us on 101 or contact Crimestoppers anonymously on 0800 555 111."
BreakingA man has died after a stabbing, say police
Essex Police has confirmed a man has died after a stabbing in Leigh-on-Sea.
A man has been arrested on suspicion of murder.
The deceased man has not been indetified by police. It comes after MP Sir David Ames was stabbed earlier today.
Conservative MP for Harlow Robert Halfon has called the events "just horrific".
Speaking on BBC Essex. he said: "David Amess is just such a wonderful man. He's funny, he's kind, he cares about the most disadvantaged in our communities.
"He loves Essex, he embodies Essex. I just feel such a sense of sadness really that this has gone on.
"He's just doing his surgery, just doing what MPs do to try to help members of the public and this happens. I feel really sad inside - deeply, deeply sad."
Sir David 'was doing his normal surgery'
Councillor John Lamb said Conservative MP Sir David Amess was just "doing his normal surgery" at the Methodist church when the stabbing happened.
He said he had been due to meet him later.
"We’re still waiting to hear how serious David is. It is very serious because we understand that they had to operate on-site," he said.
"It’s taken over two and a half hours and he’s not been moved to hospital yet. We know it’s extremely serious."
Speaking to the BBC News Channel, he added: "He’s a very hard-working MP who serves Southend and all his residents extremely well. We're all astounded by what has happened."
Amess stabbing 'dreadful news' - Sturgeon
Nicola Sturgeon has described the attack as "dreadful news".
Scotland's first minister adds that she wishes 69-year-old Sir David a quick recovery.
Councillor John Lamb, who is at the scene where Conservative MP Sir David Amess was stabbed, described him as an "amicable" family man, according to the PA news agency.
Speaking to the BBC News Channel, he added: "You're here to meet people, that is your role and you
cannot do all that on the video and so on... you have to meet them and be
prepared to meet them.
"All it means is that... you have to take the best
precautions you can to keep you and your people safe. And that's what David
does all the time... But he wanted to meet the people so he went round the
constituency."
What do we know so far?
As we've been reporting, Conservative MP Sir David Amess has been stabbed as he met with constituents earlier today.
Here's what we know about the incident at present:
What happened? The 69-year-old, who is MP for Southend West, was stabbed as he met constituents at Belfairs Methodist Church in Leigh-on-Sea.
What happened after the atack? An air ambulance was sent to the scene to treat Sir David.
Has anyone been arrested? Essex Police say they were called to reports of a stabbing in Leigh-on-Sea at 12:05 BST and arrested a man. They say they also recovered a knife and they are not looking for anyone else in connection to the incident.
What has the reaction been? Brendan Cox, whose wife, Labour MP Jo Cox, was murdered in an attack in West Yorkshire in 2016, described the stabbing of Sir David Amess as "as cowardly as it gets". Former PM David Cameron added his "thoughts and prayers are with Sir David Amess and his family".
Jo Cox Foundation 'horrified' by attack
The Jo Cox Foundation, which was set up in the wake of MP Jo Cox's murder, says that it is "horrified" to hear that Sir David Amess had been attacked.
"We are thinking of him, his family and loved ones at this distressing time," a statement from the charity reads.
Armed officers at the scene
Anthony FitchCopyright: Anthony Fitch
Armed police officers have been pictured at the scene following the stabbing of Conservative MP Sir David Amess in Leigh-on-Sea.
A man has been arrested and police are not looking for anyone else in connection with the attack.
Stabbing 'as cowardly as it gets'
Brendan Cox, whose wife, Labour MP Jo Cox, was murdered in an attack in West Yorkshire in 2016, described the stabbing of Sir David Amess as "as cowardly as it gets".
He tweeted: "Attacking our elected representatives is an attack on democracy itself. There is no excuse, no justification. It is as cowardly as it gets."
We've received our first picture from the scene at Eastwood Road North, where MP Sir David Amess was holding a constituency surgery.
Police have not confirmed the MP's condition following the attack.
Former leader's thoughts with Amess family
Conservative MP and former party leader Sir Iain Duncan Smith tweeted this shortly after news of the stabbing broke.
"My thoughts are with David Amess MP and his family at this awful time," he said.
"Praying for a full recovery following this appalling, shocking news. This angry, violent behaviour cannot be tolerated in politics or any other walk of life..."
Reaction to the attack
Former prime minister David Cameron has tweeted: "Very alarming and worrying news reports coming from Leigh-on-Sea. My thoughts and prayers are with Sir David Amess and his family."
East Ham Labour MP Stephen Timms, who was stabbed at a constituency surgery in 2010, wrote on Twitter: "Appalled to hear of the attack on [David Amess] today. I know him well and am thinking of him with very best wishes as we await further news."
Witness: 'Very distressing incident'
One witness who works nearby described seeing someone being taken out of the building and put into the back of a police car, before he was asked to leave the area.
"At that point obviously we knew something serious had happened," he told LBC.
"Within five minutes we'd been informed by someone who was actually in the building what had happened and apparently he had been stabbed quite a few times. It's very distressing, that's for sure.
"To have it next door to where you're working is obviously very upsetting and very unlike what it's like round here. It's very odd and it's very distressing, that's for sure."
BreakingSir David Amess MP stabbed
The BBC has confirmed that David Amess has been stabbed while conducting a constituency surgery in Leigh-on-Sea. Two local councillors have told us that he was the victim of an attack.
Police say a man has been arrested following a stabbing in Eastwood Road North. An air ambulance attended the incident.
Labour leader Starmer reacts to stabbing reports
The leader of the Labour Party, Sir Keir Starmer, gave his reaction to news of the attack on Twitter.
Essex Police has released the following statement after the reported stabbing at Sir David Amess's constituency surgery:
"We were called to reports of a stabbing in Eastwood Road North, Leigh-on-Sea shortly after 12.05 BST today.
"Officers were on scene shortly after, arrested a man and recovered a knife. He is currently in custody.
"We are not looking for anyone else in connection with the incident and do not believe there is an ongoing threat to the wider public.
"We want to thank the public who alerted us to the incident so quickly."
Constituency surgery held in church
Conservative MP Sir David Amess, who has been MP for Southend West since 1997, was holding a constituency surgery at Belfairs Methodist Church in Eastwood Road North, Leigh-on-Sea.
An employee of Jean's Laundry, near the church, said she did not know anything about the situation but had seen emergency service vehicles go by.
"We just saw all the police and the ambulances turning up, it was probably about 12:30 or just before then," she told the PA news agency.
Live Reporting
Edited by Emma Atkinson
All times stated are UK
Get involved
'Truly devastating' - local reporter
Ellis Whitehouse, a reporter for the Essex Live website, says he worked with Sir David for around five years and that the news is "truly devastating".
"It's a truly horrendous state of affairs and I'm just devastated," he tells the BBC - adding that Sir David was "extremely helpful" to him and his colleagues.
Speaking about the local community, he says: "I imagine this whole thing has been a real shock to everyone."
Everyone "has put their political differences aside and has really come together to support each other", he adds.
BreakingSir David Amess has died
The BBC can now confirm that the man who died this afternoon was Conservative MP Sir David Amess.
The 69-year-old, who is MP for Southend West, was stabbed as he met constituents at Belfairs Methodist Church in Leigh-on-Sea, Essex.
We'll bring you more details as we get them as only limited information has been released at this point.
Police statement in full
Here is Essex Police's statement in full:
"A man has been arrested on suspicion murder after a man was stabbed in Leigh-on-Sea.
"We were called to an address in Eastwood Road North shortly after 12.05pm today (Friday, 15 October).
"We attended and found a man injured.
"He was treated by emergency services but, sadly, died at the scene.
"A 25-year-old man was quickly arrested after officers arrived at the scene on suspicion of murder and a knife was recovered.
"He is currently in custody.
"We are not looking for anyone else in connection with this incident.
"We want to thank the public who alerted us to the incident so quickly.
"We need anyone who saw anything or has CCTV, dash cam or doorbell footage to contact us.
"If you have any information you can submit a report online at https://www.essex.police.uk or use the 'Live Chat' button to speak to an online operator between 7am-11pm.
"Please quote incident 445 of 15 October.
"You can also call us on 101 or contact Crimestoppers anonymously on 0800 555 111."
BreakingA man has died after a stabbing, say police
Essex Police has confirmed a man has died after a stabbing in Leigh-on-Sea.
A man has been arrested on suspicion of murder.
The deceased man has not been indetified by police. It comes after MP Sir David Ames was stabbed earlier today.
Harlow MP feels 'deeply, deeply sad'
Conservative MP for Harlow Robert Halfon has called the events "just horrific".
Speaking on BBC Essex. he said: "David Amess is just such a wonderful man. He's funny, he's kind, he cares about the most disadvantaged in our communities.
"He loves Essex, he embodies Essex. I just feel such a sense of sadness really that this has gone on.
"He's just doing his surgery, just doing what MPs do to try to help members of the public and this happens. I feel really sad inside - deeply, deeply sad."
Sir David 'was doing his normal surgery'
Councillor John Lamb said Conservative MP Sir David Amess was just "doing his normal surgery" at the Methodist church when the stabbing happened.
He said he had been due to meet him later.
"We’re still waiting to hear how serious David is. It is very serious because we understand that they had to operate on-site," he said.
"It’s taken over two and a half hours and he’s not been moved to hospital yet. We know it’s extremely serious."
Speaking to the BBC News Channel, he added: "He’s a very hard-working MP who serves Southend and all his residents extremely well. We're all astounded by what has happened."
Amess stabbing 'dreadful news' - Sturgeon
Nicola Sturgeon has described the attack as "dreadful news".
Scotland's first minister adds that she wishes 69-year-old Sir David a quick recovery.
Sir David an 'amicable' man
Councillor John Lamb, who is at the scene where Conservative MP Sir David Amess was stabbed, described him as an "amicable" family man, according to the PA news agency.
Speaking to the BBC News Channel, he added: "You're here to meet people, that is your role and you cannot do all that on the video and so on... you have to meet them and be prepared to meet them.
"All it means is that... you have to take the best precautions you can to keep you and your people safe. And that's what David does all the time... But he wanted to meet the people so he went round the constituency."
What do we know so far?
As we've been reporting, Conservative MP Sir David Amess has been stabbed as he met with constituents earlier today.
Here's what we know about the incident at present:
What happened? The 69-year-old, who is MP for Southend West, was stabbed as he met constituents at Belfairs Methodist Church in Leigh-on-Sea.
What happened after the atack? An air ambulance was sent to the scene to treat Sir David.
Has anyone been arrested? Essex Police say they were called to reports of a stabbing in Leigh-on-Sea at 12:05 BST and arrested a man. They say they also recovered a knife and they are not looking for anyone else in connection to the incident.
What has the reaction been? Brendan Cox, whose wife, Labour MP Jo Cox, was murdered in an attack in West Yorkshire in 2016, described the stabbing of Sir David Amess as "as cowardly as it gets". Former PM David Cameron added his "thoughts and prayers are with Sir David Amess and his family".
Jo Cox Foundation 'horrified' by attack
The Jo Cox Foundation, which was set up in the wake of MP Jo Cox's murder, says that it is "horrified" to hear that Sir David Amess had been attacked.
"We are thinking of him, his family and loved ones at this distressing time," a statement from the charity reads.
Armed officers at the scene
Armed police officers have been pictured at the scene following the stabbing of Conservative MP Sir David Amess in Leigh-on-Sea.
A man has been arrested and police are not looking for anyone else in connection with the attack.
Stabbing 'as cowardly as it gets'
Brendan Cox, whose wife, Labour MP Jo Cox, was murdered in an attack in West Yorkshire in 2016, described the stabbing of Sir David Amess as "as cowardly as it gets".
He tweeted: "Attacking our elected representatives is an attack on democracy itself. There is no excuse, no justification. It is as cowardly as it gets."
Picture from the scene
We've received our first picture from the scene at Eastwood Road North, where MP Sir David Amess was holding a constituency surgery.
Police have not confirmed the MP's condition following the attack.
Former leader's thoughts with Amess family
Conservative MP and former party leader Sir Iain Duncan Smith tweeted this shortly after news of the stabbing broke.
"My thoughts are with David Amess MP and his family at this awful time," he said.
"Praying for a full recovery following this appalling, shocking news. This angry, violent behaviour cannot be tolerated in politics or any other walk of life..."
Reaction to the attack
Former prime minister David Cameron has tweeted: "Very alarming and worrying news reports coming from Leigh-on-Sea. My thoughts and prayers are with Sir David Amess and his family."
East Ham Labour MP Stephen Timms, who was stabbed at a constituency surgery in 2010, wrote on Twitter: "Appalled to hear of the attack on [David Amess] today. I know him well and am thinking of him with very best wishes as we await further news."
Witness: 'Very distressing incident'
One witness who works nearby described seeing someone being taken out of the building and put into the back of a police car, before he was asked to leave the area.
"At that point obviously we knew something serious had happened," he told LBC.
"Within five minutes we'd been informed by someone who was actually in the building what had happened and apparently he had been stabbed quite a few times. It's very distressing, that's for sure.
"To have it next door to where you're working is obviously very upsetting and very unlike what it's like round here. It's very odd and it's very distressing, that's for sure."
BreakingSir David Amess MP stabbed
The BBC has confirmed that David Amess has been stabbed while conducting a constituency surgery in Leigh-on-Sea. Two local councillors have told us that he was the victim of an attack.
Police say a man has been arrested following a stabbing in Eastwood Road North. An air ambulance attended the incident.
Labour leader Starmer reacts to stabbing reports
The leader of the Labour Party, Sir Keir Starmer, gave his reaction to news of the attack on Twitter.
Essex Police statement
Essex Police has released the following statement after the reported stabbing at Sir David Amess's constituency surgery:
"We were called to reports of a stabbing in Eastwood Road North, Leigh-on-Sea shortly after 12.05 BST today.
"Officers were on scene shortly after, arrested a man and recovered a knife. He is currently in custody.
"We are not looking for anyone else in connection with the incident and do not believe there is an ongoing threat to the wider public.
"We want to thank the public who alerted us to the incident so quickly."
Constituency surgery held in church
Conservative MP Sir David Amess, who has been MP for Southend West since 1997, was holding a constituency surgery at Belfairs Methodist Church in Eastwood Road North, Leigh-on-Sea.
An employee of Jean's Laundry, near the church, said she did not know anything about the situation but had seen emergency service vehicles go by.
"We just saw all the police and the ambulances turning up, it was probably about 12:30 or just before then," she told the PA news agency.