UPDATE: The centre and left lanes of the Mitchell Freeway northbound have been cleared after a crash this afternoon.
The emergency lane near Erindale Road in Gwelup remains blocked.
Traffic is still expected to be slow in the area.
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READ NOWEARLIER: TWO lanes of the Mitchell Freeway northbound have been closed following a crash in which one person was injured.
A St John Ambulance spokeswoman said one person was transferred to Royal Perth Hospital under normal road conditions.
The crash is believed to have involved two cars.
Both the centre and left lanes are blocked near Erindale Road, Gwelup.