U.K. police said at least 19 people were killed in a suspected terrorist attack at a concert in Manchester, northern England, in the worst such incident on British soil since the London bombings of 2005.

Fifty people were injured in the blast, Greater Manchester Police said in a statement posted on its website. The incident happened Monday night outside the 21,000-seat Manchester Arena after a concert by Ariana Grande, a 23 year-old U.S. pop singer, that was attended by hundreds of children. No one has claimed responsibility.

“This is currently being treated as a terrorist incident until police know otherwise,” the police said in the statement.

The bombing happened in the middle of an election campaign, with Prime Minister Theresa May’s Conservative Party saying it will suspend all activities on Tuesday. It’s the latest in a series of attacks that have traumatized Europe since 2015 and comes just two months after a lone attacker left five people dead outside the Houses of Parliament in London.

“We are working to establish the full details of what is being treated by the police as an appalling terrorist attack,” May said in an emailed statement. “All our thoughts are with the victims and the families of those who have been affected.”

‘Lot of Smoke’

Witnesses told Sky News they heard a loud bang at the end of the performance. Footage posted on social media by a Guardian newspaper reporter showed a bomb disposal van driving into the area and the roads closed off by police.

“The concert had finished and we were all leaving and there was an explosion to our left and people started running,” British television actress Isabel Hodgins, who was at the show, told Sky News. “It smelled of burning and there was quite a lot of smoke as we were leaving.”

Witnesses told BBC radio there were a large number of young people at the concert. One said parents were standing on walls screaming for their children after the blast. Hotels in the city took in children while attempts were made to trace their families.

Pictures of missing teens were posted on social media by friends and relatives trying to trace them.

Some concert goers said at first they thought the explosion was caused by one of the pink balloons decorating the hall. Others reported panic as people scrambled to leave the arena.

Train services to Manchester were disrupted, according to National Rail, and Manchester Victoria station was evacuated.

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