Nineteen people are dead and around 50 others injured after reports of an explosion at an Ariana Grande concert at Manchester Arena in England.

In a statement, Greater Manchester Police said they were called to the arena at just before 10:35 p.m. local time on Monday. Authorities are telling people to avoid the area.

At the moment, the incident is being treated as a “terrorist incident until police know otherwise,” police said. U.S. law enforcement officials have been informed that the leading theory is that the Manchester Arena incident was the work of a suicide bomber, though they caution that this is preliminary information, according to a senior law enforcement official briefed on the investigation.

The wounded are being treated at six different hospitals, Greater Manchester Police Chief Constable Ian Hopkins said in a press conference. “We’re doing all that we can … as we gather information about what happened,” he said, asking people to remain vigilant.

Andy Holey, an eyewitness, told the BBC that he was waiting outside the concert and was blown over by the force of what he described as an “explosion.” When he awoke, he said he saw many casualties around him. He added that it was unclear if they were injured or dead.

Abby Barker, who attended the concert, told ABC News that Grande had just left the stage when there was a loud bang. “I looked across the arena and everyone over there started running in different directions, screaming in panic,” she said. “We all started panicking too and ran out the doors and ran down the stairs out of the arena. We got outside and children were crying their eyes out, people talking about it being a bomb/gunshots, there were many parents running towards the arena but no one knew exactly what it was.”

According to a spokesman for the British Home Office, they are holding a senior staff meeting on the Manchester incident this evening.

U.K. Prime Minister Theresa May said in a statement that they “are working to establish the full details of what is being treated by the police as an appalling terrorist attack.”

“All our thoughts are with the victims and the families of those who have been affected,” she added.

(AP)