The PM says the images of people helping others "embodies the spirit of Manchester".

She says everyone in the UK stands together with the people of Manchester at "this terrible time".

She says the terrorists will never win and "our values will always prevail".

The prime minister also says she will visit Manchester later today and chair another meeting of Cobra.

She says while we experienced the worst in humanity in Manchester we also experienced the best.

She praises the emergency services and the acts of kindness from people in Manchester.

Mrs May says a large cordon around Victoria station and Manchester Arena will remain in place "for some time".

She calls on people to give information about the attack to police.

She says the threat remains severe and a terrorist attack is still likely.

She says security services believe the attacker acted alone but they are working to find out whether he was assisted.

She says they believe they know the identity of the perpetrator but can't confirm his name.

She adds that the attack stands out for its "appalling, sickening cowardice"

She says that 22 were killed and 59 injured and many people are being treated for life-threatening injuries.

Many children and young people were killed, she says.

The prime minister says the police and security services are working to establish a full picture of what happened.

She says a single terrorist detonated an improvised explosive device near to an exit of the venue deliberately choosing time and place to cause "maximum carnage".

Prime Minister Theresa May is giving a statement about the attack after chairing a meeting of the emergency Cobra committee.

She says people have fallen victim to a "callous terrorist attack".

Today Programme
BBC Radio 4

Olivia Campbell Hardy has been missing since last night's concert.

Her mother, Charlotte Campbell, speaking on Radio 4's Today programme said "she's not been found yet" but "she can't thank people enough" for having helped her since her appeal on social media.

A passer-by who came to leave flowers outside the Manchester Arena said the city will come together: "It's the shock of it being targeted towards teenagers, I think that's what really hit home.

"But this city is really resilient and people will come together and show love."

BBC Radio 5 live

Eye-witness Emma Johnson was close to the blast at the Manchester Arena as she collected her daughter, 15, and son, 17, from the concert.

She told 5 live Breakfast: “I saw this flash of light and then there was just smoke and shrapnel everywhere, glass everywhere, people screaming.”

“You watch these things on TV, and you think ‘how awful, how terrifying’ until you are in that situation it is the worst feeling I have ever experienced.”

How to help police

• If you have any information call the anti-terrorist hotline on 0800 789321.
• Police are appealing in particular for anyone with footage or photos from the concert that may help them piece together what happened. Upload them to the UK Police Image Appeal website here., external
• Avoid Manchester city centre as emergency services are still working at the scene.

Should I give blood?

• The NHS Blood and Transplant Service is asking people not to attend blood banks today unless they have a pre-arranged appointment.
• But they are urging people to attend any pre-booked appointments over the next few days, particularly if they have blood type O negative.

How to help families of missing

• The #MissingInManchester hashtag is being used on Twitter. Friends and families are asking people to retweet pictures and share them in the hope of finding them.
• A hotline has been set up for anyone concerned about loved ones who may not have returned home. Families and friends can ring 0161 856 9400 or 0161 856 9900.

Prime Minister Theresa May is due to give a statement about the attack shortly.

Later, she is expected to travel to Manchester.

Exam boards are telling schools that they can re-arrange GCSE and A-level exams in the wake of the Manchester attack.

A joint statement from the exam boards says that it will be up to schools to decide whether exams should go ahead.

The exam boards say no students will be "disadvantaged".

"Schools and colleges affected by the bombing should contact the relevant exam boards. Students affected should speak to their teachers.‎"

You can read more about that here.

Image source, PA

Image source, Christopher Furlong

The BBC's Nafeesa Shan has been assessing the mood in Manchester the morning after the atrocity of last night.

"The train I catch to the city centre is normally heaving," she writes.

"This morning it was like a ghost service. Where they can, city commuters are keeping away."

Read more.

Liverpool City Region Metro Mayor Steve Rotheram has praised the "spontaneous acts of ordinary people" of Manchester following last night's attack at a concert in the city.

His two daughters and two nieces were at the Ariana Grande concert at the Manchester Arena.

Chris Phillips, the former head of national counter-terrorism security, told the BBC the attack had been carried out "quite professionally" and warned it was "potentially not yet over".

"I would be very surprised if there was only one suicide belt, I would be very surprised if only one set of explosives was used, and certainly I'd be really surprised if only one person was involved."