MANCHESTER, England -- At least 19 people are dead and about 50 injured in a possible terrorist incident Monday night at Manchester Arena in England, where pop singer Ariana Grande was performing, Greater Manchester Police said.
"This is currently being treated as a terrorist incident until police know otherwise," Manchester police said on Twitter.
"We can confirm there was an incident as people were leaving the Ariana Grande show last night. The incident took place outside the venue in a public space. Our thoughts and prayers go out to the victims," police said early Tuesday on Twitter.
After the initial incident, police carried out a precautionary controlled explosion nearby but the item turned out to be discarded clothing, not a "suspicious item," Greater Manchester Police said.
Investigators are looking into the possibility of a suicide bombing outside of the arena, according to a Western law enforcement official and a US law enforcement official.
Earlier police had warned people to stay away from Manchester Arena after reports of two loud explosions. The crowd was made up of mainly younger people who had come to see Grande in her first of three scheduled concerts in the UK, on her European and Latin American tour.
Ivo Delgado, a witness, told CNN he heard one explosion after the concert ended. He said there was smoke in a main corridor outside the arena seating and stage area as he and others were heading out of the building.
"It was a really big explosion. Everybody started screaming and running," he said.
Delgado said: "There were people on the floor ... There was a lot of confusion."
Social media posts from the scene showed panicked concertgoers running down the arena's stairs in an attempt to get away.
British Transport Police told CNN it was in the process of closing some transport in the area.
Video from near the scene showed a caravan of ambulances heading to the arena.
Universal Music Group, parent company for Grande's record label, Republic Records, posted a statement on Facebook.
"We are deeply saddened to learn of tonight's devastating event in Manchester. Our thoughts and prayers are with all those affected by this tragedy," the post says.
The leader of Britain's Labour Party, Jeremy Corbyn, offered support on Twitter. "Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services."
Musicians such as Ed Sheeran, Nicki Minaj and Katy Perry all offered supportive tweets.
Perry tweeted Monday that she is "Praying for everyone at @ArianaGrande's show."