A motorist has been filmed violently attacking two people on busy Bay Street in Port Melbourne.

Passers-by filmed the man as he stepped out of his car and assaulted the pedestrian and a second man.

He was later detained by onlookers in a citizen’s arrest.

It is believed the incident occurred when a pedestrian tried to cross the road at the intersection of Graham Street and Bay Street about 1pm yesterday, and was nearly hit by the man's four-wheel-drive.

Witnesses said the pedestrian gestured to the driver, who subsequently left his car and aggressively confronted him.

A good Samaritan watched the clash unfold and ran over to assist, before he was allegedly placed into a choke-hold.

“Two guys were arguing over something [before] the driver put him in a sleeper hold,” witness Andrew Volpetti said.

“He was agitated and definitely took it too far. He was in the guy’s face, nose-to-nose.”

It took five passers-by to restrain the alleged offender until police arrived to arrest him.