A presumed homeless man survived a human torch attack by three drunks on a street in central Helsinki today, but suffered severe burns, police said.

"The man, in his forties, was for some reason lying unconscious on a bench at a tram stop when two drunken men and a woman came and doused him with flammable liquid before setting him alight," Chief Inspector Juha Rautaheimo of the Helsinki police told AFP.

"Everything happened very quickly," said the officer, who added that one of the many witnesses to the scene rushed to put out the fire.

The victim, likely a local homeless man, was hospitalised with burns to 20 percent of his body but was not in life-threatening condition, he said.

Two of the attackers, all of them Finns, were arrested while the third is still on the run, said Rautaheimo, who added that the motive of the attack was still unclear and being investigated.