Here is what we know so far about the suspected terrorist attack at Manchester Arena.
UPDATE 2.30am: British Prime Minister Theresa May said her thoughts were with the victims and families of those affected in the Manchester incident, which is being treated as an "appalling terrorist attack".
Mrs May will chair a meeting of the Government's emergency Cobra committee on Tuesday following the Manchester explosion which is being treated as an "appalling terrorist attack".
The Prime Minister said the authorities were working to establish what happened at the Manchester Arena, after 19 people were confirmed dead following reports of an explosion at an Ariana Grande concert.
Mrs May said: "We 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."
A Tory source said the Prime Minister's General Election campaign was being suspended.
UPDATE 1.15am: 19 people have died after a blast tore through a pop concert at Manchester Arena in a suspected terror attack, police have said.
Greater Manchester Police said that around 50 other people were injured in the explosion at the Ariana Grande concert.
The force said in a statement: "This is currently being treated as a terrorist incident until police know otherwise."
Latest statement on incident at Manchester Arena pic.twitter.com/BEpLOan3dY— Greater Manchester Police (@gmpolice) May 23, 2017
The police update said: "Just before 10.35pm on Monday 22 May 2017, police were called to reports of an explosion at Manchester Arena.
"So far 19 people have been confirmed dead, with around 50 others injured.
"This is currently being treated as a terrorist incident until police know otherwise."
Earlier:: 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 shortly after US singer Ariana Grande’s gig finished 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."
EXPLOSION AT MANCHESTER ARENA AND EVERYONE RAN OUT SO SCARY😭 pic.twitter.com/pJbUBoELtE— ♡hannah♡ (@hannawwh) May 22, 2017
Jade Baynes, 18, from Hull, was told to run from the area by armed police after leaving the concert arena.
She said she heard loud bangs and what sounded like gunshots just after the entertainment had finished.
She added: "There were just a loud bang and a flash and everyone tried to scramble out.
"An alarm came on telling everyone to stay calm but leave as quickly as possible."
my brother just sent me this counting the police cars, please stay safe manchester hopefully they will too pic.twitter.com/szHZAZHTyA— liddy (@phanopoly) May 22, 2017
Jade and her friend Jasmine Mia, 21, also from Hull, said there appeared to be some sort of commotion in the first tier of the arena, with a number of stewards stood around the seats.
Armed police have now swamped the streets around the arena and police are moving members of the public away from the area.
Oliver Jones, 17, who attended with his 19-year-old sister, said: "The bang echoed around the foyer of the arena and people started to run.
"I seen people running and screaming towards one direction and then many were turning around to run back the other way."
Manchester’s Victoria station, which backs on to the arena, has been evacuated and all trains cancelled.
National Rail said in an online statement: "Emergency services are dealing with an incident at Manchester Arena. As Manchester Victoria is located near the arena, the station has been evacuated and all lines closed.
"Trains are currently unable to run to/from Manchester Victoria. Some trains will be cancelled throughout or start/terminate at alternative stations. Disruption is expected to continue until end of the day."
British Transport Police said: "Officers are at Manchester Arena following reports of an explosion within the foyer area of the stadium at 10.30pm this evening.
"Emergency services are at the scene and we are working to establish more information regarding the explosion and will provide further updates as soon as possible."
A spokesman for American singer Ariana Grande, who was performing at the arena, told the BBC she was okay.
The ambulance service warned people only to call "for life threatening emergencies" and said a "large number of resources" were at the incident.