Police said the attack happened about 5.45pm on Dennis Street, Dandenong when the senior constable pulled over a blue Holden Commodore.

Preliminary checks suggested the driver did not have a license and the car was not registered

Police believe the officer conducted the usual checks but before completing his work the driver attacked him. Police said the other occupants got out of the car to join the assault.

The officer suffered serious head injuries and was transported to the Dandenong hospital in a stable condition. He was released from hospital late last night.

The driver fled the scene. Police could not say exactly how many people were in the car but believe there were "several men" involved in the incident.

Victoria Police are searching for the vehicle and its occupants.