UPDATE: Police have confirmed there have been fatalities at US pop star Ariana Grande's concert at Manchester Arena in north-west England.
There are reports up to 20 people have died and hundreds may be injured. Around 21,000 people were attending the concert.
Witnesses reported hearing a "huge bang" towards the end of the show, thousands of fans then rushed towards the exits in a panic.
It is unsure if the fatalities and injuries are a result of the suspected 'blast' or from the stampede of people leaving the venue. There are unconfirmed reports 'nails' were see flying through the air after a blast.
David was outside Manchester Arena, waiting to pick up his wife and daughter who were attending the concert.
"I heard this almighty bang, then just saw people running and screaming," he said speaking to SCA Radio.
His wife told him she heard two explosions; a smaller one then a bigger one that could be heard outside.
"I asked my wife, was there any flash or smokes? She seems to think it came from behind the stage. But she never saw any flashes that would lead to anything believing it's sinister. We hope and pray that it wasn't".
Speaking to Channel 9 over the phone, Chris Pawley, who was just 20m from the stage described the sound as the "biggest explosion ever".
"We left a couple of minutes before Ariana finished her last song so we wouldn't hit all the traffic. We had just come out of the main doors of the arena, across the bridge in Victoria Station and then we heard the biggest explosion ever."
"Everyone started panicking. Our initial thought was maybe a Terrorist."
"The concert was great but the rest was one of the worst experiences of our life and we're hearing now that people have died, it's just horrible."
Central Manchester is now in lockdown as emergency crews assist the injured.
A representative for Grande has told Reuters the singer is "okay and unhurt" after the incident.
Australia's Department Of Foreign Affairs and Trade is currently working to find out if any Australians have been caught up in the tragedy.
"The Australian High Commission in London is making urgent enquiries to determine whether any Australians have been affected by the incident."