Woman critical after being hit by cement truck in Melbourne

A truck driver has been charged with drug possession and driving without a licence following a head-on crash in Melbourne's west that left a woman fighting for life.

The crash occurred at Derrimut around 12.45pm on Wednesday when a prime mover crossed a medium strip and collided with a car, police say.

A 51-year-old Derrimut woman, the car's sole occupant, was trapped in the wreck for more than 40 minutes with life threatening injuries.

She remains at the Royal Melbourne Hospital in a critical condition.

The truck driver, 49-year-old Fitzroy man Wirihana Tatana, will appear in the Melbourne Magistrate's Court on Thursday to answer multiple charges.

He is charged with causing serious injury, possessing a drug of dependence and driving with a suspended licence.

There are also two outstanding warrants relating to traffic offences.