The police department have confirmed the number of casualties to be 19 in the explosions and said that the incident is being treated as terrorist attacks until further investigation.
According to MirrorOnline, police tweeted people to "stay away from the area" and ambulances, police cars and two riot vans have been seen at the arena.
Reuters reports that emergency services are responding to the reports of "a serious incident".
"Our thoughts are with those 22 victims that we now know have died, the 59 people who have been injured and their loved ones".
Witnesses reported "panic" among thousands of concert-goers after hearing a "huge bang".
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"It's the most awful feeling ever to know your daughter is there and you can't find her, and you don't know if she's dead or alive", she said.
Manchester Mayor Andy Burnham said he will also take part in the Cobra meeting, which is set to start at 9am on Tuesday.
News agency ANI quoted unconfirmed reports saying that an unknown terror account of a possible Islamic State sympathiser tweeted about the Manchester Arena in England, hours before the blast. I lay her down, she'd got a stomach wound and possibly a broken leg.
British Prime Minister Theresa May condemned the "appalling terrorist attack" and suspended her campaign ahead of a general election on June 8.
Twitter was abuzz with video of panicked fans running out of the Manchester Arena.
ORIGINAL TEXT: An explosion was reported at Manchester Arena in the United Kingdom where an Ariana Grande concert was being held.
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U.S. media outlets reported officials in America as saying a suicide bomber was suspected as being behind the blast, although this has not been confirmed. "This is now being treated as a terrorist incident until police know otherwise".
Oliver Jones, 17, who claimed to be at the concert with his 19-year-old sister told the Guardian that he was in the toilet as people were beginning to leave after the concert when he heard a loud explosion. "It was chaotic. Everybody was running and screaming and just trying to get out of the area".
The city's Manchester Royal Infirmary Hospital was blocked off to all but essential staff due to what the facility called a major incident. People's skin and faeces were everywhere including in my hair and on my bag.
She said: "Broken. From the bottom of my heart, I am so sorry".
Train services to and from Manchester Victoria Station - located under the Arena - had been cancelled.
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