A man with a gunshot wound to his leg has driven himself, along with a friend and two children, to hospital after an alleged road rage incident north-west of Melbourne.

Victoria Police were called after two men appeared at the Ballan hospital around 5:00pm (AEST) on Sunday afternoon.

Police are still searching for a man they say tried to run a car off the road near Bacchus Marsh and when confronted, pistol whipped the driver and shot the adult passenger.

The men's children, a six-year-old boy and a three-year-old girl, witnessed the shooting.

Lee, the man who was pistol whipped, said it was a terrifying incident, particularly for the two young children.

"I was standing next to my car, he's walked over swiftly, pointing the gun in my direction and with one heavy swing, he's just gone and cracked me in the face," he said.

"After he's cracked me in the face, it's sort of stunned me, and I've then looked over to the left and he's walked around to the other side of the car where my mate was standing.

"Again he was swearing and carrying on and pointed the gun at him and shot him in the leg.

"I didn't really know how to react it all happened so fast."

Lee said his friend Cam drove to the hospital because he was dizzy from the being hit in the head.

He said Cam told the man there were children in the car.

"He was told we had kids in the car, and to sort back off and leave, he didn't listen and my mate got shot in the leg," Lee said.

Road rage incident 'worst nightmare'

Detective Sergeant Warren Chapman said the incident was "a parent's worst nightmare".

"To think that a three and a six-year-old were in the car at the same time and saw this unfold, it must've been a terrifying experience for them," he said.

"It should've been a routine drive home on a Sunday afternoon."

Detective Sergeant Chapman said police were looking for a man driving a silver Commodore.

"Persons would've seen that silver Commodore driving erratically on the Western Freeway yesterday afternoon," he said.

"It may be that some person has jotted down a registration number or seen the offender driving the motor vehicle, we encourage them to contact Crime Stoppers."