Twenty two people have been confirmed dead and 59 were injured following an explosion at an Ariana Grande concert in Manchester, England, which authorities are treating as a "possible terror incident".
Greater Manchester Police confirmed the fatalities at Manchester Arena, where thousands of people, including many children, were gathered for the pop singer's concert.
Twenty-two people were killed and 59 were injured when a lone bomber detonated an improvised explosive as the concert came to a close.
"We have been treating this as a terrorist incident and we believe that while the attack last night was conducted by one man, the priority is to establish whether he was acting alone or as part of a network," Chief constable Ian Hopkins said in a statement.
"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."
Hopkins earlier said police are working closely with the national counter terrorism policing network and UK intelligence partners.
BBC Home Affairs Correspondent Daniel Sandford reported that senior national Counter-Terrorism officers are assembling in London.
The North West Ambulance Service confirmed that paramedics took 59 people from the arena to surrounding hospitals, in addition to treating a number of "walking wounded" at the scene. Police have confirmed that the injured are being treated at six hospitals across the Greater Manchester region.
Police were called to the arena at 10:33pm on Monday night (7:33am Tuesday AEST), just after Ariana Grande had finished performing.
Authorities have warned people to stay away from the area and have cordoned off the surrounding streets.
Police have been scouring the scene for any further explosive devices. Just before 2am local time, they set off a controlled explosion in Cathedral gardens following the discovery of a "suspicious item", but it turned out to be abandoned clothing.
British Prime Minister Theresa May said in a statement: "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."
The British PM has suspended her General Election campaign following the fatal explosion, sources inside the Conservative party have said.
Liberal Democrat leader Tim Farron has also cancelled a planned campaign visit to Gibraltar.
The election is scheduled to be held in just over a fortnight, on June 8.
An eyewitness, Andy, was in the foyer near the entrance to the arena when the explosion went off and was thrown to the ground by the force of the explosion.
He told BBC 5 live that the scene was "like something out of a war film".
"When I get up and look round, there's just bodies everywhere -- I reckon 20 to 30 bodies. I can't say if some of them were dead but they looked dead.
"They were covered in blood and were really seriously hurt."
Footage posted on social media shows thousands of fans screaming as they pour out of the packed stadium. Images show the injured being helped from the scene by emergency services.
The arena is the largest in Europe, holding up to 21,000 people.
Twenty-two-year-old Robert Tempkin from Middlesbrough told the BBC: "Everyone was screaming and running -- there were coats and people's phones on the floor. People just dropped everything."
"Some people were screaming they'd seen blood but other people were saying it was balloons bursting or a speaker had been popped.
"There were lots of ambulances. I saw somebody being treated. I couldn't tell what had happened to him."
The incident comes on the fourth anniversary of the brutal murder of British Fusilier Lee Rigby, who was run over with a car before being attacked with knives and a cleaver by Islamic extremists near the Royal Artillery Barracks in London.
A music label spokesperson for Grande told Reuters that the US singer is "okay" following the explosion.
American rapper BIA (real name Bianca Landrau), who was the opening act on the night, has also posted on social media, reassuring fans that she and her team are unharmed.
Victoria Station, which is directly under the Manchester Arena, has been evacuated and no trains will run to or from the station until at least Wednesday.
Locals in Manchester have opened up their homes to people stranded with their children late at night and taxis are also taking people from the area free of charge.
The Holiday Inn Express down the road from the stadium has also reportedly taken in at least fifty unaccompanied children, who were separated from their parents in the panic following the blast.
The Director-General of Security at ASIO, Tony Sheehan, said that the Australian High Commission in London were working to determine whether any Australians had been caught up in the event.
"There is no further information about perpetrators or motives at this stage, but our agencies will be in very close contact with their UK counterparts on this tragic event," Sheehan said.
"The UK agencies will be treating this as a potential terrorism event until shown to be otherwise.
"We should all express our condolences to the families of those who have been impacted by this event."
Federal Opposition Leader Bill Shorten has described the suspected terror attack as "every parent's nightmare".
"Thinking of all those killed or hurt in the attack in Manchester. And the parents worried sick about their kids," he tweeted.
The British High Commissioner to Australian, Menna Rawlings, has recognised the "amazing" support from Australia, saying both Malcolm Turnbull and Shorten had contacted her in the wake of the attack.
Australia's Smart Traveller website has updated their travel advice for Australians to include the incident, but the overall safety level for the UK has not changed.
The Mayor of Manchester, Andy Burham, says it is "a terrible night for our great city".
"My heart goes out to families who have lost loved ones, my admiration to our brave emergency services," he said in a tweet.
This story has been updated to reflect current information, more to come.
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