Twenty-two people are dead and 59 others injured after reports of an explosion at an Ariana Grande concert at one of Europe’s largest arenas.

In a statement, Greater Manchester Police said they were called to the Manchester Arena in England just before 10:35 p.m. local time on Monday. Authorities are telling people to avoid the area.

At the moment, the incident is being treated as a "terrorist incident until police know otherwise," police said.

U.S. law enforcement officials have been informed that the leading theory is that the Manchester Arena incident was the work of a suicide bomber, though they caution that this is preliminary information, according to a senior law enforcement official briefed on the investigation.

The wounded are being treated at six different hospitals, Greater Manchester Police Chief Constable Ian Hopkins said in a press conference. "We're doing all that we can ... as we gather information about what happened," he said, asking people to remain vigilant.

The explosion happened inside of the arena’s foyer area after the concert finished, according to witnesses, who reported hearing a loud bang as they exited the arena. The venue holds about 21,000 people and is one of Europe’s largest indoor arenas, according to its website.

The concert arena is connected to the Manchester Victoria Station, the city’s second-largest train station.

The British Transport Police department said extra officers would be patrol at "key railway stations as well as on trains around the country” in the wake of the attack.

"Throughout the day, commuters can expect to see additional officers on their journey,” BTP Assistant Chief Constable Robin Smith said in a statement early Tuesday. "This will include both armed and unarmed officers.”

“As the public would expect in response to an incident such as this, extra BTP officers will be on patrol at key railway stations as well as on trains around the country,”

U.K. Prime Minister Theresa May and Jeremy Corbyn have agreed that all national campaigning in the General Election were "suspended until further notice" in the aftermath of the incident, according to the Press Association, which cited Labour officials.

May is set to hold an emergency COBRA meeting at 9 a.m. local time. The group typically meets after major incidents to plan the government’s overall response. The group -- composed of government ministers, military and security chiefs -- will also review the threat level, which is currently one below the highest possible level.

Latest statement on incident at Manchester Arena pic.twitter.com/BEpLOan3dY — G M Police (@gmpolice) May 23, 2017

VIDEO: SPECIAL REPORT: Multiple fatalities at Ariana Grande concert (ABCNews.com) More

'Everyone was just screaming': Witnesses describe chaos after reported explosion at Ariana Grande concert

Concertgoers reported hearing a loud bang at the end of the concert and attendees rushed toward the exit.

PHOTO: Police and other emergency services are seen near the Manchester Arena after reports of an explosion, May 22, 2017. (Joel Goodman/LNP/REX/Shutterstock) More

Eyewitness Karen Ford told the BBC, "The lights had come up everyone was just getting out and walking towards the stairs, when all of a sudden this huge sound, which sounded like an explosion went off."

She added: "Everyone just stopped and turned around, and then somebody shouted 'it’s a bomb' and everyone just started running. Everybody was trying to push people up the stairs. There was a lot of children there without parents. There was no one to calm them down so everyone was just screaming, crying and pushing."

PHOTO: Police and other emergency services are seen near the Manchester Arena after reports of an explosion, May 22, 2017. (Joel Goodman/LNP/REX/Shutterstock) More

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