Explosion kills at least 22 in Manchester concert

A blast on Monday night at a concert in the northern English city of Manchester where US singer Ariana Grande had been performing left at least 22 people dead and about 59 injured in what British police said was being treated as a terrorist incident.

Prime Minister Theresa May said the incident was being treated as a terrorist attack.

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

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

As the situation on the ground is still fluid and the events have been moving fast, there's a lot of information coming out of Manchester. Here is what we know so far:

Videos that capture the panicking crowds fleeing the blast area in the Manchester Arena were posted on social media shortly after the incident.

A witness who attended the venue said she felt a massive explosion as she was leaving the concert.

"We were making our way out and when we were right by the door there was a massive explosion and everybody was screaming," Catherine Macfarlane said.

"It was a huge explosion - you could feel it in your chest. It was chaotic. Everybody was running and screaming and just trying to get out of the area."

A spokesman for the pop singer's record label said that she was "okay."

The singer later tweeted saying that she was "broken" and "sorry" over the incident.

Witnesses reported that many children were at the concert.

Paula Robinson, 48, from West Dalton about 40 miles east of Manchester, said she was at the train station next to the arena with her husband when she felt the explosion and saw dozens of teenage girls screaming and running away from the arena.

"We ran out," Robinson told Reuters. "It was literally seconds after the explosion. I got the teens to run with me."

Robinson took dozens of teenage girls to the nearby Holiday Inn Express hotel and tweeted out her phone number to worried parents, telling them to meet her there. She said her phone had not stopped ringing since her tweet.

"Parents were frantic running about trying to get to their children," she said. "There were lots of children at Holiday Inn."

Celebrities including Taylor Swift, Katy Perry and Chris Brown were quick to offer their condolences for those who lost their lives at the concert.

Britain is on its second-highest alert level of "severe" meaning an attack by militants is considered highly likely.

British counter-terrorism police have said they are making on average an arrest every day in connection with suspected terrorism.

For more on this, Sara Firth joins us from London.