A alleged booze-fuelled argument has left a mother in custody and a father fighting for life in hospital after he was flung from a moving car in Melbourne’s south-west.

Damien Osbourne allegedly told his friends to “look out for the kids” before he latched onto the side door of his partner’s vehicle.

Mr Osbourne suffered catastrophic head injuries after he was flung from his partner Tara’s McConchie moving vehicle in Point Cook just before 2.30am today.

Police believe the couple had been drinking at a friend’s house when an argument spilled onto the street, with their three children, all aged under 11, still inside.

As the 36-year-old father clung to the family’s Holden Jackaroo, police allege Ms McConchie hit the accelerator.

He held onto the car for about 60 metres before he was thrown onto the road.

“She was just screaming ‘he’s gonna die, he’s dying … somebody help’,” witness Jill Grimison told 9News.

Neighbours cradled the former defence force member’s head and called Triple Zero.

“He wasn’t conscious, he was breaking but it was almost as if he was snoring,” Ms Grimison said.

“There was an argument going on. They were both very intoxicated.”

Detective Sergeant Mark Amos said the bottom line was to not drink and drive.

“Don’t ride on the side of a car outside of it. It’s not designed for that,” he said.

As her partner of eight years was taken to hospital, Ms McConchie was taken into custody.

“What is going to happen to those three kids? Who’s going tell them that bad news? I don’t want to do it. I can’t think of anything worse,” Sergeant Amos said.

Ms McConchie remains in custody and is yet to be questioned by major collision investigators.

She is undergoing a medical evaluation.

Mr Osborne has spent most of the day in surgery at the Royal Melbourne Hospital. He is now in a serious condition.