UPDATE: Police in Manchester have confirmed they are treating an apparent 'explosion' at Ariana Grande's concert as a terrorist incident, until they can rule otherwise.
They have confirmed 19 people have died and around 50 others are injured. It's believed the attack was carried out by a suspected suicide bomber in the foyer of Manchester Arena.
Around 21,000 people were attending the concert when the incident happened.
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 seen flying through the air after a blast.
Chris Parker, 33, was walking through Victoria Station towards the box office when the explosion went off.
Speaking to The Sun, he said he saw at least six people seriously injured on the floor.
"There were nuts and bolts flying everywhere and human flesh. It was just one bang and a white flash. I treated a woman called Pauline. I've got blood on my hands."
"It was like a war zone inside where the box office is. There looked to be at least six people potentially fatally wounded. I saw one woman's leg off. It is mayhem."
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 Triple M's The Grill Team.
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."
A controlled explosion was also carried about nearby after a suspicious item was discovered.
A representative for Grande has told Reuters the singer is "okay and unhurt" after the incident.
While her music label Universal Media Group put a statement on their Twitter page.
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."