An off-duty police officer feared he was going to die during an alleged vicious attack by a gang of armed youths after he came to the aid of a beleaguered bus driver.

Victoria Police Senior Constable David Thorne was getting off a bus at Waverley Gardens Shopping Centre in Mulgrave, at 1.30pm last Thursday, when he noticed a group of teenagers giving the driver a "hard time". But when he spoke up, the youths turned on him.

Senior Constable David Thorne was allegedly assaulted after he intervened in a dispute at a bus stop. Credit:Eddie Jim

“As I got off the bus I said something like 'ease up guys, he’s just doing his job',” Senior Constable Thorne told The Age.

“One of the young males pulled out a box cutter, like a Stanley knife, and a female pulled out some kind of pointy weapon. I tried to diffuse the situation by taking the box cutter out the young man's hand ... that's when I got king-hit from behind with something sharp, I don’t know what.”