How the Manchester attack unfolded and what we know about the bombing Here is what we know about how the attack took place.

 -- The deadly attack carried out by a suspected suicide bomber in Manchester, England, on Monday night left emergency personnel scrambling to secure the area, tend to the wounded and reunite lost children with their families.

Here's a timeline of events for the attack:

10:35 p.m. local time Monday: Emergency services received more than 240 calls to the Manchester Arena, which seats 21,000 people.

Concertgoers reported hearing a loud bang at the end of the concert just as Grande left the stage. Thousands of attendees rushed toward the exit.

Photos from the scene show wounded victims on the floor in the venue or being carried out by others.

Locals in Manchester begin opening up their homes with the hashtag #RoomforManchester.

Police say the explosion is being treated as a terrorist incident.

1:30 a.m.: Police conduct a controlled explosion in Cathedral Gardens, a few minutes from the stadium. They later confirm that what was thought to be a suspicious item was abandoned clothing.

4:06 a.m.: The North West Ambulance Service announces that more than 60 ambulances responded to the scene.

11:54 a.m.: Police confirm that a man was been arrested at the Arndale Center but say the arrestee is not believed to be connected to the attacks.

3:51 a.m.: Ariana Grande tweets that she is "broken" and "so sorry" in response to the attack.

What we know about the attack

Twenty-two dead, 59 wounded

Children are among the dead, including an 8-year-old girl

The attack was claimed by ISIS

The suspected attacker has been identified as 22-year-old Salman Abedi by police

U.K. Prime Minister Theresa May called the attack "sickening"

The wounded and the missing

The wounded are being treated in several different area hospitals and some of them are battling life-threatening injuries, authorities said.

Many people are still missing and an emergency hotline has been set up for people concerned for “loved ones who may not have returned home," police said. Facebook activated its global "safety check" feature in the wake of the deadly attack.

The investigation

Police have said they believe the attack was carried out by “one man,” 22-year-old Salman Abedi, who died at the scene after he detonated an "improvised explosive device.” Police and intelligence officials immediately launched an investigation after Monday's incident.

On Tuesday, Manchester police also announced the arrest of a 23-year-old suspect in connection with the attack.

So far, they have not said if there were any accomplices in planning or carrying out the attack or if any suspects have been linked to terrorist organizations.

The terror group ISIS claimed responsibility for the attack on Tuesday in an Arabic-language news release.

“The priority is to establish whether he was acting alone or as part of a network,” Ian Hopkins, chief constable of Greater Manchester Police, said of the attacker at a press conference Tuesday.

“Our priority is to work with the national counterterrorism policing network to establish more details about the individual who carried out this attack," he added.

Police have not identified the nationality of the person behind the attack, but a former director of the security service M16 told BBC earlier that the bomber was likely already known to security services.

Prime Minister calls the attack "sickening" after an emergency meeting on Tuesday

U.K. Prime Minister Theresa May called the suspected terrorist attack "sickening" and "appalling." She held an emergency meeting with government ministers, military and security chiefs to plan the government’s overall response.

The prime minister announced Tuesday evening that the country's threat level had increased to critical, meaning another attack is imminent.

May said the attacker deliberately targeted children and young people "who should have been enjoying one of the most memorable nights of their lives."

"We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherished but as an opportunity for carnage," May said.

The concert venue, which holds about 21,000 people, is one of Europe’s largest indoor arenas, according to its website, and it is connected to the city’s second-largest train station.

Ariana Grande's tour

It’s not clear if Grande, who has two concerts scheduled in London later this week, will go on with her world tour as planned.

The pop star‘s "Dangerous Woman" tour was originally scheduled to end on Sept. 21 in Hong Kong.

Grande was not hurt in the attack, but she tweeted last night that she was feeling “broken.”

ABC News' Emily Shapiro contributed to this report.