The 72-year-old musician, best known for his 1969 hit Spirit in the Sky, was a passenger in a car that hit a motorcycle on the Northern California road.

Sergeant David Derczo of the California Highway Patrol tells local newspaper The Press Democrat that the motorcycle's driver, 20-year-old Ihab Usama Halaweh, died at the scene, while his passenger was critically injured.

Greenbaum's driver was not hurt, but the singer is now fighting for his life in hospital.

The cause of the accident has yet to be revealed, but Derczo confirms alcohol is not suspected to be a factor.