Ysgol Dyffryn Aman - which translates as Amman Valley School in English - is a bilingual comprehensive school in Ammanford, Carmarthenshire, in south-west Wales.
The school, which educates 11 to 18-year-olds, has about 1,450 pupils and 270 in its sixth form.
It's about 20 miles (32km) from the centre of Swansea and 60 miles (97km) from Cardiff.
It comes under Carmarthenshire County Council.
BBCCopyright: BBC
'Parents say children being held in lockdown'
Tomos Morgan
BBC News in Ammanford
Parents of children at Dyffryn Aman school say they have spoken to their children and that the students are being held in lockdown in their classes.
It’s believed that whatever incident took place has ended, with three ambulances and two air ambulances leaving the scene around half an hour ago.
There is a significant police presence.
Hundreds of parents are waiting at the entrances for their children.
None of the parents I’ve spoken to have been told what exactly has happened inside Dyffryn Aman.
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BreakingOne arrested and three injured in school incident, police confirm
Dyfed-Powys Police confirms it is dealing with an incident at a school in the Amman Valley.
In a statement, the force said: "Three people have been injured and are receiving treatment.
"One person has been arrested and we are not looking for anyone else in connection with this incident.
"Emergency services remain at scene and the school has been closed while investigations continue.
"We are working closely with the school and Carmarthenshire County Council.
We are aware that there is footage of the incident currently circulating on social media.
"We would ask that this is removed to avoid contempt of court and distress to those affected.
We would ask the people do not speculate while there is a police investigation ongoing."
'We've seen the air ambulance leave'
Meleri Grug Williams
I'm here outside Ysgol Dyffryn Aman where we understand there are reports of a number of people having been injured.
We haven't got any more information at the moment, but we've also seen the air ambulance leaving the premises.
There are a number of police here and many parents are waiting for their children to be able to leave school - we understand they're being kept safe there for now.
BBCCopyright: BBC
Local MP expresses concern at stabbing reports
Local MP Jonathan Edwards, who is MP for Carmarthen East and Dinefwr, has expressed his concern on social media.
"Thoughts are with everyone back home and with the authorities responding," he wrote.
BBCCopyright: BBC
'You send your child to school thinking they'll be safe'
Lisa Barrett, whose daughter attends Ysgol Dyffryn Aman school in the west Wales town of Ammanford, says her daughter texted her saying her secondary school was in lockdown.
She told the BBC there are reports that a number of people have been stabbed.
"It is really worrying," said Ms Barrett.
"You hear from your child saying someone has been stabbed you don't know what to do for the best.
"You just don't expect it, you send your children to school and think they will be safe.
"It is comforting to know they are locked in the classrooms though."
Mrs Barrett has said she has heard nothing from the school.
"It's just a waiting game," she said. "I don't know whether to go down there or not."
Emergency services outside the school
Here's the scene at the school in west Wales this Wednesday lunchtime.
It shows a police vehicle in attendance, as well as two air ambulance helicopters which landed on grass outside Ysgol Dyffryn Aman in Ammanford, Carmarthenshire,
It comes amid reports of a stabbing at the school with worried parents saying the school is in lockdown.
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Emergency services are at the school, responding to an incidentImage caption: Emergency services are at the school, responding to an incident
Two air ambulances at school
Emergency services are in attendance at an incident at a secondary school in west Wales.
There have been reports of a stabbing at Ysgol Dyffryn Amman in Ammanford, Carmarthenshire on Wednesday.
Wales Air Ambulance have confirmed two helicopters attended the incident, with one now en route to University Hospital of Wales in Cardiff.
Concerned parents have posted online that the school is locked down, with pupils being held in their classrooms.
Live Reporting
Catriona Aitken, Peter Shuttleworth and Oliver Slow
All times stated are UK
Where is Ysgol Dyffryn Aman?
Ysgol Dyffryn Aman - which translates as Amman Valley School in English - is a bilingual comprehensive school in Ammanford, Carmarthenshire, in south-west Wales.
The school, which educates 11 to 18-year-olds, has about 1,450 pupils and 270 in its sixth form.
It's about 20 miles (32km) from the centre of Swansea and 60 miles (97km) from Cardiff.
It comes under Carmarthenshire County Council.
'Parents say children being held in lockdown'
Tomos Morgan
BBC News in Ammanford
Parents of children at Dyffryn Aman school say they have spoken to their children and that the students are being held in lockdown in their classes.
It’s believed that whatever incident took place has ended, with three ambulances and two air ambulances leaving the scene around half an hour ago.
There is a significant police presence. Hundreds of parents are waiting at the entrances for their children.
None of the parents I’ve spoken to have been told what exactly has happened inside Dyffryn Aman.
BreakingOne arrested and three injured in school incident, police confirm
Dyfed-Powys Police confirms it is dealing with an incident at a school in the Amman Valley.
In a statement, the force said: "Three people have been injured and are receiving treatment.
"One person has been arrested and we are not looking for anyone else in connection with this incident.
"Emergency services remain at scene and the school has been closed while investigations continue.
"We are working closely with the school and Carmarthenshire County Council. We are aware that there is footage of the incident currently circulating on social media.
"We would ask that this is removed to avoid contempt of court and distress to those affected. We would ask the people do not speculate while there is a police investigation ongoing."
'We've seen the air ambulance leave'
Meleri Grug Williams
I'm here outside Ysgol Dyffryn Aman where we understand there are reports of a number of people having been injured.
We haven't got any more information at the moment, but we've also seen the air ambulance leaving the premises.
There are a number of police here and many parents are waiting for their children to be able to leave school - we understand they're being kept safe there for now.
Local MP expresses concern at stabbing reports
Local MP Jonathan Edwards, who is MP for Carmarthen East and Dinefwr, has expressed his concern on social media.
"Thoughts are with everyone back home and with the authorities responding," he wrote.
'You send your child to school thinking they'll be safe'
Lisa Barrett, whose daughter attends Ysgol Dyffryn Aman school in the west Wales town of Ammanford, says her daughter texted her saying her secondary school was in lockdown.
She told the BBC there are reports that a number of people have been stabbed.
"It is really worrying," said Ms Barrett.
"You hear from your child saying someone has been stabbed you don't know what to do for the best.
"You just don't expect it, you send your children to school and think they will be safe.
"It is comforting to know they are locked in the classrooms though."
Mrs Barrett has said she has heard nothing from the school.
"It's just a waiting game," she said. "I don't know whether to go down there or not."
Emergency services outside the school
Here's the scene at the school in west Wales this Wednesday lunchtime.
It shows a police vehicle in attendance, as well as two air ambulance helicopters which landed on grass outside Ysgol Dyffryn Aman in Ammanford, Carmarthenshire,
It comes amid reports of a stabbing at the school with worried parents saying the school is in lockdown.
Two air ambulances at school
Emergency services are in attendance at an incident at a secondary school in west Wales.
There have been reports of a stabbing at Ysgol Dyffryn Amman in Ammanford, Carmarthenshire on Wednesday.
Wales Air Ambulance have confirmed two helicopters attended the incident, with one now en route to University Hospital of Wales in Cardiff.
Concerned parents have posted online that the school is locked down, with pupils being held in their classrooms.