Road rage behind Melbourne freeway smash

A driver in "a road rage" who was yelling out his window and swerving between lanes was behind a head-on crash on a major Melbourne freeway, a witness claims.

Four men were injured when a car crashed through the wire barrier of the Monash Freeway in Wheelers Hill, colliding with another car about 6.30am on Friday.

A man who witnessed the crash says the car that caused the accident had been all over the road.

"(The driver) had his window down and was verbally abusing the car beside him," Ross, who did not provide a surname, told 3AW on Friday.

He said the driver was "swerving and trying to get closer and closer" before losing control of his car and going "across the barrier and straight into the front of the car going outbound".

"It was road rage for sure," he said.

A Victorian Police spokeswoman told AAP it was too early to determine the cause of the crash but investigators would look at all avenues, including road rage.

The injured men are currently in hospital in a stable condition, Ambulance Victoria spokesman Paul Bentley said.