MANCHESTER, England -- UK police arrested a 23-year-old man in Manchester in relation to the Ariana Grande concert attack, according to the Greater Manchester Police Department.
At least 22 people, including children, were killed in a bombing at the concert in Manchester, in the deadliest attack on British soil since the 2005 London bombings.
British Prime Minister Theresa May chaired an emergency Cabinet meeting Tuesday and said the explosion was being treated as an "appalling terrorist attack."
'I want her home'
The explosion rocked the Manchester Arena at around 10:30 p.m. (5:30 pm ET) as Grande fans, many of them young teenagers and children, left the venue.
Confusion ensued as people fled in a panic for safety, and the sound of wailing sirens soon cut through the smoky air outside.
Witnesses described chaotic scenes of children crying and parents desperately trying to find their children as cell phone signals faltered in the deluge of calls.
Some parents still haven't heard from their children.
"We've tried everything we can. They're telling us to wait by the phones," Manchester resident Charlotte Campbell told CNN as she waited for news on her daughter, Olivia.
The 15-year-old had gone to the concert with a friend and neither have been in contact, she said.
"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."
Grande, who had just finished the first of three scheduled UK performances when the blast hit, was not injured. She tweeted about her devastation several hours later: "broken. from the bottom of my heart, i am so so sorry. i don't have words."
Police: IED used
Greater Manchester Police Chief Constable Ian Hopkins said that victims were being taken to eight hospitals and confirmed that children were among the dead.
"We believe the attacker was carrying an improvised explosive device which he detonated," he said.
"We have been treating this as a terrorist incident and we believe at this stage that the attack was carried out by one man."
Hopkins added that police were investigating whether the attacker was part of a larger network or plot.
As many as 400 police were deployed 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.
Trump calls attackers 'losers'
US President Donald Trump slammed the attack, saying that terrorists were "losers."
"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. We stand in absolute solidarity with the people of the United Kingdom," Trump said.
"So many young beautiful innocent people living and enjoying their lives murdered by evil losers in life. I won't call them monsters because they would like that term. They would think that's a great name. I will call them from now on losers because that's what they are."
"This wicked ideology must be obliterated."
A US Department of Homeland Security statement said it was "closely monitoring" the situation.
'I brought my baby home'
The incident happened shortly after Grande had left the stage, according to witnesses.
Coral Long, the mother of a 10-year-old concertgoer, told CNN's Hala Gorani that 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 her daughter was devastated.
"For her to be 10 years old and witness something like that is just horrific."
Social media posts from the scene showed concertgoers running down the arena's stairs in an attempt to flee.
Karen Ford had taken her 13-year-old daughter to the concert and described "mayhem" on the street.
"There were children crying, trying to get in touch with parents, parents on their phones trying to contact their kids," she said Monday night.
"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.
Katy Perry tweeted Monday that she is "Praying for everyone at @ArianaGrande's show."