British police said 22 people including some children were killed in a suicide attack carried out by one man after a Ariana Grande concert in Manchester on Monday.
“We believe, at this stage, the attack last night was conducted by one man,” Manchester Chief Constable Ian Hopkins said.
“The priority is to establish whether he was acting alone or as part of a network. The attacker, I can confirm, died at the arena. We believe the attacker was carrying an improvised explosive device which he detonated causing this atrocity,” Constable Ian Hopkins added.
Two loud explosions were reportedly heard near the ticket office of the arena.
A video posted on Twitter showed fans, many of them young, screaming and running from the venue. Dozens of parents frantically searched for their children, posting photos and pleading for information on social media.
Britain is on its second-highest alert level of “severe” meaning an attack by militants is considered highly likely.
British counter-terrorism police have said they are making on average an arrest every day in connection with suspected terrorism.
“Please stay away from the area. Emergency services responding to serious incident at Manchester Arena. Avoid the area,” Greater Manchester Police said in a series of tweets.
Manchester Arena, the largest indoor arena in Europe, opened in 1995 and has a capacity for 21,000 people, according to its website. It is a popular concert and sporting venue.
A spokesman for Ariana Grande’s record label said that the singer was “okay”. A video posted on Twitter showed fans screaming and running out of the venue.
The UK’s Network Rail said train lines out of Manchester Victoria station, which is close to the concert venue, were blocked.
In March, a British-born convert to Islam ploughed a car into pedestrians on London’s Westminster Bridge, killing four people before stabbing to death a police officer who was on the grounds of parliament. He was shot dead at the scene.