UPDATED: Ariana Grande 'Broken' After Deadly Bombing At Concert

"broken. from the bottom of my heart, i am so so sorry. i don't have words."

Ariana Grande tweeted these 16 words early Tuesday in the wake of the worst terror attack in Britian in more than a decade.

At least 22 people were killed and nearly 60 injured when a lone suicide bomber set off explosives outside Manchester Arena only minutes after Grande's concert ended.

British prime minister Theresa May called it "a callous terrorist attack ... that targeted some of the youngest people in our society with cold calculation."

The blast happened shortly after 10:30 p.m. local time as fans were leaving Grande’s show.

MORE: Drake Says He's "Crushed" By Terror Attack

Fan-shot video posted online reveals that an announcer took to the 21,000-capacity venue's P.A. to try to calm panicked fans.

“Ladies and gentlemen, please take your time. There is no reason to bunch up. There’s no problems here. Just take your time and keep exiting the building," the announcer said.

“Thank you for coming and having a good time tonight. Everything is fine. Please take your time exiting the building.”

Dave Thompson / Getty Images

Within hours, Greater Manchester Police tweeted that the incident was "being treated as a terrorist incident until police know otherwise."

The BBC reported that paramedics were treating “shrapnel-like injuries.”

The broadcaster quoted Robert Tempkin as saying: "Everyone was screaming and running, there were coats and people's phones on the floor. People just dropped everything.

MORE: Country Stars Share Shock, Grief Over Manchester Terror Attack

"Some people were screaming they'd seen blood but other people were saying it was balloons busting or a speaker had been popped.”

Manchester is a little more than 300 kilometres north of London.

Grande's publicist Joseph Carozza confirmed late Monday night that the pop star was safe. TMZ cited sources as saying the singer was "inconsolable".

Scooter Braun, Grande's manager, shared a statement on Twitter:

Concert promoter Live Nation said in a statement: "We are deeply saddened by this senseless tragedy and our hearts and thoughts are with those impacted by this devastating incident."

Grande is currently on the European leg of her Dangerous Woman Tour. She is scheduled to do concerts in London on Thursday and Friday — but it’s not known if those shows will go ahead.

"Ariana is due to perform at The O2 on Thursday and Friday and we will advise as soon as we can as to the status of those shows," read a tweet from London's O2 Arena. "Along with everyone else, we are shocked and saddened by the terrible tragedy in Manchester. Our thoughts are with all those affected."

There are reports Grande will cancel all remaining shows on her European tour.

A message on the Manchester Arena website said “the incident took place outside the venue in a public space. Our thoughts and prayers go out to the victims.” There are no concerts scheduled at the arena until Thursday, when British group Take That is scheduled to perform.

Canada's Celine Dion is scheduled to perform at Manchester Arena on June 25.

Canadian artists were among those taking to social media to express shock and sadness.

Shawn Mendes tweeted: "I am truly so sorry about what has happened in Manchester tonight. Unthinkable events. All my love to families affected." He later added: "This isn't what music is all about. Completely heartbroken."

Justin Bieber tweeted simply: "#PrayForManchester"

"Manchester you are in our hearts, thoughts and prayers," read a tweet from Nickelback. "Sending all love and light to those affected. Stay strong."

Jann Arden said: "Big love to all of those at the @ArianaGrande show in Manchester. I feel completely gutted. #livemusic."

Singer Scott Helman tweeted info for blood donations and other services in Manchester. "My thoughts with everyone in Manchester," he wrote.

Here's a look at tweets from a few music stars:

This story has been updated.