Blast occurred on Monday night at a concert in the English city of Manchester where U.S. singer Ariana Grande had been performing left at least 19 people dead and more than 50 injured in what British police said was being treated as a terrorist incident.
Police said they were responding to reports of an explosion and that there were a number of confirmed fatalities and others injured at the arena, which has a capacity for 21,000 people.
A witness who attended the concert said she felt a huge blast as she was leaving the arena, followed by screaming and a rush as thousands of people trying to escape. Witnesses reported that many children were at the concert.
Manchester Arena, the largest indoor arena in Europe, opened in 1995 and is a popular concert and sporting venue.
A spokesman for Ariana Grande, 23, said the singer was “okay”.
A video posted on Twitter showed fans, many of them young, screaming and running from the venue.
Britain is on its second-highest alert level of “severe” meaning an attack by militants is considered highly likely.
British Prime Minister Theresa May will hold a meeting of the country’s top security committee at 9 am (0800 GMT) on Tuesday after the explosion.
May said on Tuesday that authorities were working to establish the details of the blast which killed 19 and injured dozens, adding that it was being treated as an “appalling terrorist attack”.
“We are working to establish the full details of what is being treated by the police as an appalling terrorist attack,” she said in a statement. “All our thoughts are with the victims and the families of those who have been affected.”
There is no indication of threat to US music venues.
The US Department of Homeland Security said it was closely monitoring the situation in Manchester, England.
The department said in a statement it had “no information to indicate a specific credible threat involving music venues in the United States.”
“However, the public may experience increased security in and around public places and events as officials take additional precautions,” according to a statement.