UPDATE: A WITNESS to a fight in Melbourne’s CBD where a motorbike rider pulled a gun on his assailant claims road rage sparked the attack.

Police are hunting the motorcyclist who shot a firearm after he was assaulted by a shirtless pedestrian while stopped at a red light, on the corner of Lonsdale and Spencer streets, about 7.25pm on Sunday.

Investigators have not been able to confirm what started the fight between the two men, who are not known to each other.

But witness Kiefer Brown said he believed the rider may have collided with the pedestrian before the scuffle, which lasted about two minutes.

“The two men were throwing punches at each other for ages, the cars behind them beeping as they tried to turn onto Spencer Street,” Mr Brown said.

“The man in the motorbike gear got knocked over, as he was getting up I heard a bang and he held the gun to the other man then walked to his motorbike.”

Other witnesses had told police they believed the rider shot into the air but Mr Brown said he saw him direct the gun to the shirtless assailant, who police believe was under the influence of drugs or alcohol.

“It was so scary, I’ve been around farms and hunting guns my whole life but hand guns are a whole different ball game,” Mr Brown said.

The rider, who stored the black hand gun in the waist of his pants, then jumped back on his motorbike and drove south down Spencer St.

Mr Brown said he returned to the scene a few days later to check the wall behind the fight but could find no sign of a bullet.

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The pedestrian, a 24-year-old Thai national living in Melbourne, has been charged with affray and assault.

The rider is described as Asian with a medium build and short dark hair.

It’s believed he was riding a 2008-2010 Suzuki GXSR 6000 and wearing a black, white and red leather jacket, dark pants and white shoes.

Images have been released of the rider in the hope police can gather further information.

Given the busy intersection and time of day, it’s believed a number of people witnessed the incident who are yet to speak with police.

Contact Crime Stoppers on 1800 333 000 or at crimestoppersvic.com.au