The rescue helicopter has been sent to a motorcycle crash on the Kwinana Freeway in Stake Hill.
The crash happened near the Lakes Road turnoff just after 11am on Monday.
Emergency crews are at the scene.
Police believe the rider has suffered serious injuries.
The Kwinana Freeway is closed southbound at Mandjoogoordap Drive.
Kwinana Fwy CLOSED southbound at Mandjoogoordap Dr to Lakes Road, Stake Hill due to a serious crash AVOID THE AREA more info: https://t.co/EmkqlV8vZ1 #perthtraffic
— Main Roads WA (@Perth_Traffic) December 3, 2018