UPDATE: 22 killed in terror attack at UK pop concert

There were scenes of panic as Grande's audience of youthful fans fled the 21 000-capacity venue after what eyewitnesses described as a "huge bomb-like bang" in the foyer area at the end of the concert.

A fleet of ambulances was seen rushing to the venue and bomb disposal teams were dispatched soon after, as city residents opened up their doors to stranded concert-goers after train services were shut down.

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"So far 19 people have been confirmed dead, with around 50 others injured. This is currently being treated as a terrorist incident until police know otherwise," police said in a statement earlier.

British Prime Minister Theresa May condemned the "appalling terrorist attack".

"All our thoughts are with the victims and the families of those who have been affected," she said in a statement.

The first unconfirmed reports of an explosion emerged shortly after 2145 GMT on Monday.

Gary Walker from Leeds told BBC Radio 5 Live he was hit by shrapnel in his foot and his wife sustained a stomach wound as they waited for their daughters to come out of the concert.

"We heard the last song go and then suddenly there was a massive flash and then a bang and smoke," he said.

Manchester Arena said the incident "took place outside the venue in a public space".

Police carried out a controlled explosion in a small park near the venue a few hours after the blast but said the item turned out to be only abandoned clothes.

Manchester residents opened up their homes to people who could not get home after the incident, sending messages with the hashtag #RoomforManchester.

Ariana Grande's manager, Scooter Braun reacted soon after the incident. 

While other A-listers took to Twitter to react to the tragedy. 

Listen to the full bulletin below.