The explosion occurred around 10:33 p.m. local time near the ticket office outside the arena, Chief Constable Ian Hopkins said. The attack was carried out by a lone suspect who detonated an improvised explosive device who died at the scene, Hopkins said.
According to the SITE Intel Group, ISIS has claimed responsibility for the attack.
Eyewitness Andy Holy told the BBC that he was blown through a door at the arena, noting that the “whole building shook” when the bomb went off.
“Whoever has done it, has done it on a kids concert,” he said.
British security services believe that Salman Abedi, who died in the blast, carried out the attack, CBS News and the Associated Press report. He was known to British authorities, U.S. officials tell the news outlets.
The Daily Telegraph reports that he was born in Britain to Libyan parents.
Police said at least 22 people, including some teenagers, died and approximately 59 were injured in the attack, the Associated Press reports. Greater Manchester Police said they have arrested a 23-year-old man in connection with the incident, according to the AP.
“We have been treating this as a terrorist incident and we believe, at this stage, the attack last night was conducted by one man,” Hopkins said before news of the arrest broke. “The priority is to establish whether he was acting alone or as part of a network.”
CBS News reported that the alleged bomber traveled to the arena via train and detonated the bomb as people were leaving.
“Broken. From the bottom of my heart, I am so so sorry. I don’t have words,” Grande tweeted.
In a statement to PEOPLE, the singer’s rep said Grande is “okay” following the explosion.
“We are further investigating what happened,” the rep added.
Among the many extending their condolences to victims and their families is President Donald Trump, who said in a recent address from Bethlehem, Israel, that the United States stands “in absolute solidarity with the people of the United Kingdom.”
“I extend my deepest condolences to those so terribly injured in this terrorist attack and to the many killed and the families – so many families – of the victims,” he said.
In the midst of the chaos, social media users began circulating the hashtag #RoomForManchester to alert stranded people to places where they could stay for the night.
Cab drivers also turned their meters off for the evening to transport concertgoers to safety.
A local hotel reported taking in more than 50 youths, some of whom were waiting to be reunited with parents and guardians.
Many parents have not seen or heard from their children and are using traditional and social media to try to track them down.