A number of people have died and others were injured in a reported explosion at Manchester Arena during a pop concert, police say.
Witnesses reported hearing a "huge bang" at the venue during an Ariana Grande gig on Monday evening.
Greater Manchester Police said there are already a "number of confirmed fatalities and others injured" and emergency services are at the scene after "reports of an explosion".
The area around the arena was swamped with police and emergency services. Approach roads have been closed by police.
Witnesses said they heard two loud bangs inside the arena and coming from where the bars are located.
Manchester's Victoria station, which backs onto the arena, has been evacuated and all trains cancelled.
One fan at the concert described how the explosion hit the venue as fans were leaving the building.
Majid Khan, 22, said: "I and my sister, along with a lot of others were seeing Ariana Grande perform at Manchester Arena, and we were all exiting the venue when around 10.40-10.45pm-ish a huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena.
"It was one bang and essentially everyone from the other side of the arena where the bang was heard from suddenly came running towards us as they were trying to exit Trinity Way and that was blocked so everyone was just running to any exit they could find as quickly as they could.
"Everyone was in a huge state of panic, calling each other as some had gone to the toilet whilst this had gone off, so it was just extremely disturbing for everyone there."