MANCHESTER, England -- Police have named 22-year-old Salman Abedi as the suspected bomber. He is believed to have died in the powerful blast.
While police say they believe the attacker was working alone, police said they were investigating whether the attacker was part of a larger network or plot. Although ISIS claimed the bombing, the terror group did not mention a name and did not post a photo or provide any additional details.
ISIS says "a soldier of the caliphate planted bombs in the middle of Crusaders gatherings" then detonated them.
The Islamic State group said one of its members carried out the Manchester attack that killed 22 people Monday night.
The group claimed that "30 Crusaders were killed and 70 others were wounded," higher than the totals confirmed by authorities in Manchester.
Manchester police said they have arrested a 23-year-old man in South Manchester in relation to the attack and the first named victim of the attack was Georgina Callander, 18, a student at Runshaw College.
Police said they believe a man carrying explosives acted as a lone attacker and died in the powerful blast that shook part of the cavernous Manchester Arena as concertgoers streamed out after the American pop star's last song.
"It is now beyond doubt that the people of Manchester and of this country have fallen victim to a callous terrorist attack. An attack that targeted some of the youngest people in our society with cold calculation," British Prime Minister Theresa May said after chairing an emergency Cabinet meeting Tuesday.
Police on Tuesday morning evacuated a large shopping center in Manchester. They said a man was arrested there but it "is not currently believed to connected to last night’s attacks."
July McKenzie, who was shopping when the Arndale shopping center, said: "We were just in the shop and could hear people screaming and security guards telling everybody to get out."
Some people left the scene in tears, while others waited outside the mall.
The Arndale center was rebuilt after an IRA bombing in 1996.
Greater Manchester Police Chief Constable Ian Hopkins confirmed that children were among the dead and that victims were being taken to eight hospitals.
"We have been treating this as a terrorist incident and we believe at this stage that the attack was carried out by one man," he said.
Police are investigating whether the attacker was part of a larger network or plot.
Images from the scene show people running in a panic down stairs to escape the arena amid the relentless screams of frightened children and young teenagers. Some parents say their children are still missing.
Greater Manchester Mayor, Andy Burnham, described the attack as "our darkest of nights."
"Manchester is today waking up to the most difficult of dawns. It is hard to believe what has happened here in the last few hours and to put into words the shock, anger and hurt that we feel today. These were children, young people and their families that those responsible chose to terrorize and kill. This was an evil act," he said.
Grande, who had just finished the first of three scheduled UK performances, tweeted about her devastation several hours later: "broken. from the bottom of my heart, i am so so sorry. i don't have words."
As many as 400 police were deployed in Manchester overnight, Hopkins said early Tuesday, and a CNN journalist saw a heavy armed police presence in parts of the city, particularly outside the Royal Infirmary Hospital where several victims are being treated.
London will also see a heavier police presence Tuesday as the country's terror alert remains at "severe."
The explosion rocked the arena at around 10:30 p.m., and the sound of wailing sirens cut through the smoky aftermath of the blast soon after.
Crying children and parents desperately tried to find each other as cell phone signals faltered in the deluge of calls, witnesses said.
Manchester resident Charlotte Campbell told CNN as she was still waiting for news on her 15-year-old daughter, Olivia. "We've tried everything we can. They're telling us to wait by the phones," she said.
Olivia had gone to the concert with a friend and neither have been in contact.
"Her dad is out looking ... It's the most horrible feeling ever, to know your daughter is there and you don't know whether she's dead or alive.
"I want her home and I want her safe. ... I just want her to walk through the door."
Coral Long, the mother of a 10-year-old concertgoer, told CNN they were getting ready to leave the arena when they heard a loud bang from the left side of the arena that sent the large crowd running. "How we weren't crushed to death is a miracle."
She said that her daughter was devastated. "For her to be 10 years old and witness something like that is just horrific."
Karen Ford, who had taken her 13-year-old daughter to the concert, described "mayhem" on the street.
"I brought my baby home, which some people won't be (able to do) tonight."
A nearby hotel became a focal point for parents searching for their children who had been at the concert. Some hotels opened their doors to people who could not get home due to an area lockdown. Taxis and local people offered free rides to those affected.
A Czech woman who was at the concert said that “there was almost no security check, rather zero. They let us get in without any check if we have anything with us.”
Nikola Trochtova told the Czech public radio that “the only thing they were interested in was if we had any bottles of water with us. They almost didn’t check our bags, they didn’t take a look.”
She says she was leaving the venue when she heard an explosion at the entrance, but learned the details only after returning to her hotel.
A US Department of Homeland Security statement said it was "closely monitoring" the situation.
Queen Elizabeth released the following statement Tuesday morning:
The whole nation has been shocked by the death and injury in Manchester last night of so many people, adults and children, who had just been enjoying a concert.
I know I speak for everyone in expressing my deepest sympathy to all who have been affected by this dreadful event and especially to the families and friends of those who have died or were injured.
I want to thank all the members of the emergency services, who have responded with such professionalism and care.
And I would like to express my admiration for the way the people of Manchester have responded, with humanity and compassion, to this act of barbarity.