Shocking moment a driver involved in a car rollover RUNS away from the scene down the side of a busy highway

A man involved in a car crash that left one vehicle flipped onto its roof bizarrely fled the scene and was filmed running down a busy highway.

Investigations are underway in Dandenong, in Melbourne 's southeast, after two cars collided on the Monash Freeway at about 1.25pm on Saturday.

The crash sent what appeared to be a white sedan onto its roof, with the vehicle seen completely smashed from the collision.

The driver of one of the cars involved was seen standing on the side of the highway with blood dripping from one of his knees.

He reached underneath the white car to grab something before he suddenly fled the scene.

Onlookers filmed the man run over to the other side of the freeway, before he jogged down the highway.

He eventually jumped a fence on the side of the road, disappeared into nearby bush and remains on the run.

Victoria Police confirmed they were investigating the incident. It's unclear what car the man who fled the scene was driving.

'It's believed two vehicles collided on Monash Freeway about 1.25pm,' a spokeswoman said.

'The driver of one of the vehicles fled the scene. The driver of the other vehicle was not seriously injured.'

Anyone with information, CCTV or dash cam footage is urged to call Crime Stoppers on 1800 333 000.