More than two dozen school children are in hospital after a horror crash on their way to a space camp in the United States.

The school bus, carrying 27 students, was travelling to Melbourne Airport when it collided with a truck on the Western Highway in Bacchus Marsh.

The bus rolled down an embankment around 3.15am.

One teenage girl has been airlifted to hospital with serious injuries.

The male truck driver is also seriously injured and has been taken to hospital.

The other students, four adults onboard, and the bus driver, have been taken to hospital for observation.

Image: 9News