UPDATED 2:20pm British Prime Minister Theresa May says her thoughts are with the victims and families of those affected in the Manchester Arena blast.

At least 19 people are dead and many others injured after the incident at the end of an Ariana Grande concert at 10.30pm Monday.

The Prime Minister is set to chair a meeting of the government's emergency Cobra committee following the Manchester explosions.

She said the authorities are working to establish what happened.

"We are working to establish the full details of what is being treated by the police as an appalling terrorist attack," she said early on Tuesday.

"All our thoughts are with the victims and the families of those who have been affected."

A Tory source said the prime minister's campaign for the June 8 election is being suspended.

Labour Party leader Jeremy Corbyn has tweeted, labelling it a terrible incident.

He said his thoughts are with all those affected and the brilliant emergency services.

Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services.

— Jeremy Corbyn (@jeremycorbyn) May 22, 2017