Update: A man in his 70s was flown to Royal Perth Hospital after a serious crash in Pinjarra on Monday afternoon.
The RAC rescue helicopter was deployed to assist at the incident on South Western Highway, near the Adelaide Road intersection.
It is believed the man was the rider of a motorcycle that collided with a car.
He arrived by helicopter to the hospital just after 3.30pm with serious leg injuries.
The driver of the vehicle is assisting police with their inquiries.
Earlier: A motorcycle rider has been rushed to Royal Perth Hospital by St John's Ambulance. The extent of their injuries are still unknown.
Main Roads have advised South Western Highway is closed in both directions, prior to Adelaide Road, as authorities work to clear the crash.
Motorists are being asked to seek an alternative route and avoid the area.
Mandurah's authorities have rushed to the scene of a car crash in Pinjarra on Monday afternoon.
It is believed the crash happened on South Western Highway, just after 2pm on April 22.
Police confirmed one vehicle and one motorcycle were involved but had no further information.
St John's Ambulance are in attendance. The extent of the injuries are still unknown.
More as it comes to hand.