Video footage of a man and woman being bashed in a vicious attack at a Melbourne karaoke bar has been released.

The couple in their 20s were drinking at the Elizabeth Street bar early on January 11 when they were assaulted.

Footage of the attack shows a 25-year-old man being punched and stomped on by a group of men until he was unconcious on the floor.

The man's girlfriend can be seen trying to protect him on the ground.

A man is then seen to grab her by the hair and throw her to the floor, before she is punched and kicked by the group.

Shortly before the brawl, the couple was sitting at a table with their attackers.

Detective Senior Constable Matt Folvig said it was unclear what started it, but words were exchanged beforehand.

"Apparently they've just said something that was disagreed with and they've just turned on the pair," he said.

Police released images and CCTV footage in the hope of identifying the people involved.

Anyone with information is urged to contact Crime Stoppers.