Police are investigating a serious crash at Gawler overnight.

Police were called to the scene at Top Gawler Road about 10:50pm, after a Holden Commodore sedan failed to negotiate a right-hand bend in the road.

The car then ran off the verge and crashed head-on into a tree.

The man driving was flown to the Royal Hobart Hospital in a serious condition.

He was the sole occupant of the car and was wearing a seatbelt.

The cause of the crash remains under investigation.