Driver critical and 'car in a million pieces' after smash

The driver of a station wagon which split apart after hitting a tree is in a critical condition in hospital this evening.

Police say the 26-year-old is "lucky to be alive" after his car left the road north of Melbourne CBD.

The man was heading west when he lost control of the vehicle on Broadmeadows Road in Westmeadows about 4am this morning.

The Holden SS Commodore station wagon split in half after hitting a gum tree, with the front half continuing on for another 50 metres.

Emergency crews found the driver "hanging half in and half out" of the wreck.

Police said the car had been travelling "at a rate of knots" and described the car as being "in a million pieces".

Neighbours told 9NEWS they heard "a loud bang that shook the house".

A bystander performed CPR on the man before crews arrived on the scene.

Officers praised his actions, which they say almost certainly saved the driver's life.

A witness, identified only as Scott, said: "The man was working on him for about ten minutes, saying 'Don't go' and repeating his name."

He was taken to Royal Melbourne Hospital in a critical condition.

Police are appealing for witnesses to the accident.

The road was slippery but officers are investigating if speed was a factor and if the car was stolen.

Sgt David Brockway said: "The driver is without doubt lucky to be alive".