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."
She said it looked like one of the cars had hit a fence as a result of the crash.
Traffic was backing up, and there were multiple emergency services at the scene - she counted three police cars, two ambulances and two fire engines.
