Police are investigating a collision between a truck and school bus in Bacchus Marsh early this morning (Wed.).

The collision occurred on the Western Hwy, near the intersection of Condons Lane, causing the bus to roll down an embankment about 3.15am.

One teenage girl will be airlifted to hospital with serious injuries.

The male truck driver will be taken to hospital by road with serious injuries.

The bus contained 27 female students, four adults and the bus driver – all will be taken to hospital for observation.

The Melbourne-bound lanes of the Western Hwy are expected to remain closed for several hours and motorists are urged to take an alternative route.

Any concerned parents seeking information regarding their children are asked not to attend the scene and to instead call Ballarat Police Station on 5336 6000.

Police are investigating the circumstances surrounding the collision and urge any witnesses or anyone with dashcam footage to contact Crime Stoppers on 1800 333 000 or submit confidential report at www.crimestoppersvic.com.au