A 26-year-old man has been airlifted to Royal Perth Hospital after the motorcycle he was a passenger on crashed in Margaret River.
Officers heard the motorcycle crash just outside the Margaret River Police Station at 10pm.
Police believe the Harley Davidson motorcycle hit the curb before hitting a small tree.
Firefighters assisted police until St John’s Ambulance officers arrived.
The 28-year-old driver of the motorcycle received minor injuries and was taken to Margaret River Hospital.
The pillion passenger received serious injuries and was airlifted to Royal Perth Hospital by the RAC Rescue Helicopter.
Police are investigating the circumstances surrounding the crash and would like to speak to anyone who saw it.
Anyone with any information can call Crime Stoppers on 1800 333 000.