Emergency Services have cleared a six-car prang blocking all lanes on the Kwinana Freeway northbound.
The crash occurred around 10.30am near Russell Road in Success.
Both lanes remained closed until 12pm as emergency services worked to clear the area.
A Main Roads spokeswoman said at 12.30pm traffic was still heavy back to Anketell Road.
Four people received minor injuries in the crash and were taken to Fiona Stanley Hospital for treatment.
#KwinanaFwy northbound after #RussellRd, Success - BOTH LANES BLOCKED - access via left emergency lane - crash #perthtraffic
— Main Roads WA (@Perth_Traffic) September 15, 2017