All in-bound lanes on the Monash Freeway were blocked during peak-hour traffic after an horrific crash that has left a teenage girl in hospital with life-threatening injuries.

She was a passenger in a car that crashed into a concrete pillar at Mulgrave just after midnight.

A second teenage girl has been taken to hospital with serious injuries.

The driver of the vehicle, a man aged in his 40s, has non-life threatening injuries.

The crash prompted the closure of all in-bound lanes of the Monash Freeway until nearly 7.30am.

Police are investigating the cause of the single-vehicle smash.