The RAC Rescue Helicopter is on its way to a truck rollover on the Brand Highway near Gingin.
The crash happened about 8.45am near Airfield Road, about 12km south of Gingin.
According to police, it appears the trailer of a truck may have hit a car. It is unknown how many people were involved in the crash.
Brand Highway has been closed in both directions.
St John Ambulance crews are also at the scene of a car and truck crash in West Perth, at the intersection of Thomas and Hay streets.
The crash occurred just before 9am. One person is believed to be unconscious and a nurse at the scene is assisting.
Emergency crews are also on their way to Bakers Hill, where a person is trapped in their vehicle after hitting a tree.
More to come