A car has rolled over on a bridge in Nangeenan, 15km west of Merredin.
Emergency services are at the scene and the RAC Rescue helicopter is en route to the crash.
The vehicle rolled over on Great Eastern Highway near Nangeenan North Road on Cohn Creek Bridge about 7am.
A person is believed to be trapped.
The driver is understood to have sustained serious injuries in the accident.A police spokesman said the crash had left traffic totally blocked on the bridge until further notice and road users should find an alternative route.