As British Prime Minister Theresa May upgrades the United Kingdom’s terror alert to ‘critical’, stories of heroism in the midst of one of the country’s worst terror attacks are emerging.

At least 22 people died and a further 59 were injured when a suicide bomber targeted fans leaving one of pop star Ariana Grande’s concerts in Manchester on Tuesday morning (AEST).

Islamic State claimed responsibility for the worst attack on British soil since the 2005 suicide bombings, while the bomber believed to be responsible was named as 22-year-old UK-born Salman Abedi.

On Wednesday morning, Ms May warned a further attack on UK soil was “expected imminently” and hundreds of military personnel would be deployed to protect key sites.

But amid the darkness emerged stories of bravery and selflessness shown by so-called ‘angels’ who witnessed the horrific nail bomb attack.

A GoFundMe page has raised more than $A36,000 for homeless man Chris Parker, 33, who was begging in the foyer of the arena when the bomb went off.

“It knocked me to the floor and then I got up and instead of running away my gut instinct was to run back and try and help,” Mr Parker told The Sun UK.

“I saw a little girl … she had no legs. I wrapped her in one of the merchandise T-shirts and I said, ‘Where is your mum and daddy?’ She said, ‘My dad is at work, my mum is up there’.”

Mr Parker also tended to a badly injured woman who died in his arms.

“She was in her 60s and said she had been with her family,” he said.

“I haven’t stopped crying.”

Mr Parker’s bravery made headlines in the UK, prompting his estranged mother to reach out to him.

Jessica Parker posted a plea for her homeless son to get in touch with her to her Facebook page.

“This is my son who has been estranged from me for a long while. I had no idea he was homeless but he was extremely brave last night,” she wrote.

“Please get in touch with me Chris Parker.”

Stephen Jones, 35, was sleeping rough near Manchester Arena when he heard the bomb go off.

“It’s just instinct to go and help if someone needs your help and it was children,” he told ITV News.

“It was a lot of children with blood all over them — crying and screaming … We were having to pull nails out of their arms and a couple out of this little girl’s face.”

https://www.youtube.com/watch?v=dds65GFQafA

Paula Robinson was near Manchester Victoria station when she saw dozens of teenage girls running towards her.

She and her husband acted quickly to shepherd the young concertgoers into a nearby Holiday Inn to keep them safe.

“We have got about 50 kids with us waiting to be picked up, they are safe we will look after them,” she posted on social media.

“Please repost for any parents with children at M.E.N. We have taken as many kids as we can to Holiday Inn. We will keep them safe and stay with them.”

Paula Robinson helped scared concertgoers to find shelter. Photo: Facebook

Ariana Grande’s mother Joan was in the front row at her daughter’s concert when the bomb went off, prompting her to start moving nearby fans to safety backstage.

Witnesses told TMZ that Joan, along with Ariana’s security, ushered as many as 10 children backstage so they could stay safe until it was possible to exit the arena.

Victims of the attack include eight-year-old Saffie Rose Roussos, 18-year-old Georgina Callander, 28-year-old John Atkinson,15-year-old Olivia Campbell and Merseyside girl Megan Hurley.

Several people remain unaccounted for.