Twenty-two people, including children, have been killed and 59 injured in a suicide attack at a Manchester Arena.
Video footage showed people running from the venue after the suicide bomb attack immediately at the end of an Ariana Grande gig yesterday.
The blast happened in the foyer at 22:35 BST.
The blast was reported to have hit the foyer of the building.
Theresa May has called the act one of “appalling, sickening cowardice”.
Mrs May said, “All terrorist attacks are terrible, but this stands out for its cowardice”.
Police said the lone male attacker, who died in the blast, detonated a homemade bomb.
Chief Constable Ian Hopkins said it was “the most horrific incident” the city had experienced.
He said the “fast-moving investigation” was now working to establish whether the attacker “was acting alone or as part of a network”.
Sixty ambulances attended the incident and those wounded are being treated at six hospitals around the city.
Relatives are using social media to hunt for missing loved ones, and an emergency number, 0161 856 9400, has been set up.
Senior counter-terrorism officers are assembling in London and are liaising with the Home Office.
Network Rail said train lines out of Manchester Victoria station, which is close to the concert venue, were blocked.
Victims have been taken to six hospitals across the Manchester area.
Police have carried out a “controlled explosion’’ in the Cathedral Gardens area but the item destroyed was not suspicious.
A bomb disposal unit has just arrived outside the Manchester Arena. Can also hear sniffer dogs being brought out of the vans pic.twitter.com/SgTPZxMLyg
— Chris Slater (@chrisslaterMEN) May 22, 2017
Greater Manchester Police tweeted to urge people to stay away from the area.
Concertgoers, bloodied and in tears, were helped by emergency services outside the gig and armed police were seen patrolling the arena.
Prime Minister Theresa May has said her thoughts are with the victims and families of those affected in “what is being treated by the police as an appalling terrorist attack”
Labour leader Jeremy Corbyn and Liberal Democrat leader Tim Farron have expressed their sympathies for the victims.
Robert Tempkin, 22, from Middlesbrough, said: “Everyone was screaming and running, there were coats and people’s phones on the floor. People just dropped everything.
“Some people were screaming they’d seen blood but other people were saying it was balloons busting or a speaker had been popped.
“There were lots of ambulances. I saw somebody being treated. I couldn’t tell what had happened to him.”