Emergency services are at the scene of a truck rollover on Brookton Highway in Roleystone.
The truck, believed to be a water carrier, rolled near Peet Road just after 2pm.
A police spokesman said the crash happened on a blind bend on a hill.
He said diesel was spilling from the truck and firefighters had been called to the site.
St John Ambulance officers are attending to the male driver of the truck. The extent of his injuries is not yet known.
Parts of the highway are currently blocked and representatives from Western Power and Main Roads WA are at the scene.