Twenty-two people, including children, are dead and dozens injured after a terrorist bombing branded a "barbaric attack " tore through young music fans at a concert in Manchester.
Children are feared to be among those killed and wounded in the blast at the Manchester Arena which police are treating as a "terrorist incident".
Condemning the atrocity, Home Secretary Amber Rudd said: "This was a barbaric attack, deliberately targeting some of the most vulnerable in our society - young people and children out at a pop concert."
She added: "The great city of Manchester has been affected by terrorism before. Its spirit was not bowed; its community continued.
"This time it has been a particular attack on the most vulnerable in our society - its intention was to sow fear - its intention is to divide. But it will not succeed."
Police have not said what caused or who was behind the atrocity, although unconfirmed reports have suggested it was carried out by a suspected suicide bomber.
Witnesses reported hearing a "huge bomb-like bang" at around 10.30pm on Monday, as fans were leaving the arena shortly after a show by Ariana Grande finished, and described glass and metal nuts on the floor.
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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.
Grande, the US singer who finished performing 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.
:: 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.
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 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.
Speaking last night, before the number of fatalities rose to 22, 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.