A 31-year-old and a 36-year-old pillion were riding a Honda trailbike on Mockridge Road, Clarendon Vale, when the pillion came off the bike.

The 31-year-old continued driving before he hit guttering on the right-hand side of the road, and crashed.

The incident happened about 11.15pm.

While the rider was wearing a helmet, his passenger was not wearing any safety gear and suffered significant head injuries and abrasions to his body and limbs.

They were taken to the Royal Hobart Hospital.

Police believe alcohol and speed were contributing factors to the crash.