Just moments before a nail bomb ripped through Manchester Arena, a homeless man had been stationed in the foyer begging concertgoers for help.

But a split second later, roles were dramatically reversed.

Chris Parker, 33, recalls picking himself up from the ground where he was knocked by the blast, The Telegraph reported.

"Instead of running away my gut instinct was to run back and try to help," said Mr Parker.

"I heard a bang and within a split second I saw a white flash, then smoke and then I heard screaming.

"There was people lying on the floor everywhere. I saw a little girl ... 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 said he suspected the girl's mother had died, and said a woman who appeared to be in her 60s with serious head and leg injuries passed away in his arms.

The story is one of two accounts of homeless men stepping in to help in the immediate moments after the terror attack, prompting public fundraising campaigns for the men who have since been hailed "heroes without capes".

Stephen Jones, who had been sleeping near Manchester Arena, also told British television network ITV that he pulled nails out of victims, as he entered the bomb site and encountered many children covered in blood, crying and screaming.

"We were having to pull nails out of their arms and stuff and a couple out of this little girl's face," Mr Jones said.

"Some lady, she got cut from her side here, so my mate had to hold her legs up and then an ambulance guy came and a fireman and they assisted after that. We just held her legs up because we thought she was just going to bleed right out."

Mr Jones said it was his first instinct to help.

"Just because I'm homeless it doesn't mean that I haven't got a heart and I'm not human still," he said.

"They needed the help, I'd like to think that someone would come help me if I needed the help."

About $1500 has been raised so far for Mr Jones via a gofundme campaign, with the organiser promising to track down him down via a homeless shelter.

An even bigger amount has been raised for Mr Parker - about $43,000 by Wednesday night. The organiser of that campaign is still trying to track him down via the journalists who reported the story.

Mr Parker has reportedly been homeless for about a year, one of around 189 sleeping rough in Manchester following a dramatic spike in homelessness in the city.