The hero tradie who ran into the Melbourne bank inferno to save injured victims.

A tradesman has been hailed a hero for his efforts to save victims of Melbourne bank explosion on Friday morning.

A 21-year-old man allegedly doused himself in petrol and set himself alight inside a Commonwealth Bank building in Springvale around 11.30am, causing an explosion that injured 27 people.

Six of the 27 people were taken to hospital to be treated for their injuries, including the 21-year-old male, who is in a critical condition and under police guard, Channel Nine reported.

One other person remains in a critical condition in hospital and four others have serious burns.

Ashley Atkin-Fone was laying pipes in a nearby laneway when he heard an explosion followed by screams.

“This kid comes running out, screaming his head off, with skin hanging off everywhere,” Mr Atkin-Fone told Nine News.

“I ran across the road to Optus, grabbed the fire extinguisher and tried to put the fire out.”

Mr Atkin-Fone risked injury from smoke inhalation when he entered the building to see if anyone needed to be evacuated.

“I was four metres inside choking and just shouting, “Is anybody inside?”‘ he said.

He also began trying to put out the flames before emergency service arrived.

“There were four people getting blasted [with glass] along the street,” he told the Herald Sun.

The tradesman didn't appear to think twice about the act, saying that he "had to" help.

"What would you do? Instincts just kicked in," Mr Atkin-Fone said.