"Ariana Grande had just gone behind the curtain and the lights came up when there was this massive bang and a big cloud of smoke,” a concert-goer told The Guardian.
Witness Harry Johnson told a local radio station that when people heard the explosions, they ducked for cover as fast as possible.
"People were just looking around and no-one really knew what to do. Then there was just screaming and shouting," he said. "There was no space between anyone. Everyone was squished together trying to get out. It took around a minute to get out."
The explosion was reported “within the foyer area” of the venue about 10:30 p.m., according to the British Transport Police. However, a tweet from Manchester Arena said the explosion took place “outside the venue in a public space.”
The cause of the explosion was unclear, but Manchester police said on Twitter that “this is currently being treated as a terrorist incident until police know otherwise.”
We'll keep you updates as more information arrives.
This article previously appeared on WHO.