Ambulances had taken another two people with moderate injuries to hospital.
Diversions were being established and motorists were asked to avoid the area.
The crash occured near the settlement of Matamau, opposite some paddocks belonging to the Holmes'.
"I heard a very big bang," Eileen Holmes said. "I saw a car at an angle, and some other cars stopped. People were trying to open the door of the car but they couldn't."