Twenty two people were killed and 59 people were injured in the Manchester Arena attack on Monday night, Greater Manchester Police chief constable Ian Hopkins said.
A suicide bomber has killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester.
Some 59 people were also injured when the blast caused by an improvised explosive device carried by the attacker detonated at the Manchester Arena.
Announcing that the death toll had risen, Greater Manchester Police chief constable Ian Hopkins said: "What I can confirm is that there are children among the deceased."
He said: "This has been the most horrific incident we have had to face in Greater Manchester and one that we all hoped we would never see.
"Families and many young people were out to enjoy a concert at the Manchester Arena and have lost their lives.
"Our thoughts are with those 22 victims that we now know have died, the 59 people who have been injured and their loved ones.
"We continue to do all we can to support them."
Mr Hopkins said a "fast-moving investigation" had established the attack was conducted by one man, although detectives are working to establish if he was "was acting alone or as part of a network".
"The attacker, I can confirm, died at the arena.
"We believe the attacker was carrying an improvised explosive device which he detonated, causing this atrocity."
Police were called to reports of an explosion at the Manchester Arena at 10.33pm, shortly after US singer Ariana Grande had finished her performance.
Victims described being thrown by the blast that scattered nuts and bolts across the floor.
More than 240 calls were made to the emergency services, with responders including 60 ambulances flooding the area.
More than 400 police officers were deployed as part of the operation, with a visible presence remaining on the streets of Manchester on Tuesday.
The dozens of victims injured in the attack are being treated at hospitals across Greater Manchester, and a hotline has been set up for those with concerns over loved ones who remain unaccounted for.
A large cordon remains in place around the arena and nearby Manchester Victoria Station, which was evacuated during the incident and remains closed, while forensic investigators gather evidence.
The Prime Minister has condemned the "appalling" incident and General Election campaigning has been suspended.
Downing Street said a meeting of the Government's emergency Cobra committee is expected to take place at around 9am on Tuesday morning chaired by Theresa May.
Ariana Grande, the US singer who had finished performing just minutes before the blast, said she had been left "broken" by the events.
Greater Manchester Police Chief Constable Ian Hopkins said they are treating the blast as a "terrorist incident until we have further information".
If confirmed as terrorism it would be the worst attack in the UK since 56 people were killed in the 7/7 London bombings in 2005.
As investigators begin to piece together what happened, here is a summary of events so far:
- Police said around 50 people were injured, while North West Ambulance Service said 59 casualties had been taken to six hospitals around the city. Sixty ambulances attended the incident.
- US media outlets reported officials in America as saying a suicide bomber was suspected as being behind the blast, although this has not been confirmed.
- Home Secretary Amber Rudd described it as a "barbaric act", while Mrs May said her thoughts are with those affected by the "appalling" incident.
- Officers carried out a controlled explosion on a second suspect item, which they later said was abandoned clothing.
Witnesses reported hearing a "huge bomb-like bang" at around 10.30pm on Monday, as fans were leaving the arena shortly after the show finished and described glass and metal nuts on the floor.
Gary Walker, from Leeds, was with his wife in the foyer waiting to pick up his two daughters who were at the concert.
"I was waiting for the kids to come out. We heard the last song, and quite a few people were flooding out and then suddenly there was a massive flash and then a bang, smoke," he told BBC Radio 5 Live.
"I felt a bit of pain in my foot and my leg. My wife said, 'I need to lie down'. I lay her down, she'd got a stomach wound and possibly a broken leg.
"I was about three metres from the actual explosion. I am surprised I got away so lightly."
Mr Walker said the explosion was by the door in the foyer, next to the merchandise, and that glass and metal nuts were left on the floor. He said he lay down next to his wife for up to an hour, until she was stretchered on a table to an ambulance.
His daughter Abigail, who was still in the auditorium with sister Sophie at the time of the explosion, said: "I had to make sure I had my sister. I grabbed hold of her and pulled hard. Everyone was running and crying.
"We were just trying to figure where everyone was. It was absolutely terrifying."
Abigail and Sophie contacted their parents by mobile phone, a moment Mr Walker described as "fantastic news".
One fan, Majid Khan, 22, described the explosion and ensuing panic.
"A huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena," he said.
"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."
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."
The area around the arena was swamped with police and emergency services and approach roads were closed.
Manchester's Victoria station, which backs on to the arena, was evacuated and all trains and trams cancelled.
Grande, who was unhurt in the incident, later tweeted: "broken. from the bottom of my heart, i am so so sorry. i don't have words."
Her management team, SB Projects, praised the actions of Manchester's emergency services.
They said: "Words cannot express our sorrow for the victims and families harmed in this senseless attack.
"We mourn the lives of children and loved ones taken by this cowardly act.
"We are thankful for the selfless service tonight of Manchester's first responders who rushed toward danger to help save lives.
"We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers."
Sir Richard Leese, leader of Manchester City Council, said: "This is an absolutely horrifying incident and our thoughts are with everyone affected, especially those who have lost loved ones or been injured and traumatised.
"If it is confirmed this was a terrorist attack it is a monstrous act but also a deeply futile one. Manchester is a proud and strong city and we will not allow those who seek to sow fear and division to achieve their aims."
North West Ambulance Service said it had taken 59 casualties to various hospitals and treated a number of walking wounded at the scene.
Mr Hopkins said: "At around 10.33pm we received reports of an explosion at Manchester Arena in the city centre.
"This was at the conclusion of the Ariana Grande concert.
"Currently, we have 19 people confirmed to have lost their lives in the explosion and around 50 casualties that are being treated at six hospitals around Greater Manchester.
"My thoughts are very much with those who have been injured and lost their lives and their loved ones at this terrible time, we are doing all we can to support them.
"We are currently treating this as a terrorist incident until we have further information, we are working closely with national counter-terrorism policing network and UK intelligence partners.
"This is clearly a very concerning time for everyone. We are doing all that we can, working with local and national agencies to support those affected as we gather information about what happened last night."
An emergency number was established for those concerned about loved ones - 0161 856 9400.
More on the incident in Manchester: