A man is fighting for his life after his vehicle was struck by a car that police believe may have sped through a red light at a major intersection in Melbourne's south-east.

Key points: The driver and sole occupant of one vehicle is in a critical condition

The driver and sole occupant of one vehicle is in a critical condition All six people in the other vehicle were taken to hospital, one with life-threatening injuries

All six people in the other vehicle were taken to hospital, one with life-threatening injuries Speed may have been a factor in the collision, police said

The man was driving north on Springvale Road shortly before 5:00am when he was hit by a car travelling east along the Princes Highway, police said.

Witnesses have told police the eastbound car was speeding and ran a red light at the time of the crash.

Police said they were trying to determine if it had been stolen.

The car was carrying six people, including a woman in her 20s who Ambulance Victoria said suffered life-threatening injuries to her head, chest and legs.

It is believed she is now in a stable condition.

The driver and sole occupant of the northbound vehicle, a Parkdale man in his 40s, was taken to the Alfred Hospital in a stable condition, but is now listed as being in a critical state.

Police were trying to determine if the eastbound car had been stolen. ( ABC News )

Superintendent John Fitzpatrick said the "heavy impact" of the collision meant the northbound car was pushed a significant distance across the intersection.

Springvale Road was closed in both directions and the Princes Highway outbound for much of the morning as police carried out investigations.

"If you have a look at the scene and where the debris has been strewn across, there's a fair bit of investigation that needs to take place to reconstruct it," Superintendent Fitzpatrick said.

The five other occupants of the eastbound car, aged in their mid-teens and early 20s, were taken to hospital in a stable condition with head, leg and back injuries.

Superintendent Fitzpatrick said some people in the car were not wearing seat belts.

"Anytime that you've got a sedan that's got the capacity to hold five people safely carrying six people is irresponsible," he said.

"You shouldn't really do it."