Police said there were three people in each car and some had suffered serious injuries.

The RAC rescue helicopter and local emergency services attended.

Medical staff assessed the injured people on the road side, but there were no air-lifts to Perth.

South West Traffic Division first class constable Michael Byrne said a white sedan was heading north on the bypass, then turned right on to Raymond Road towards Collie.

It crashed into a car travelling south towards Bunbury.

He said there were three witnesses to the crash who were driving behind the sedan.

South Bound traffic was blocked off and diverted through Australind.

More in the Bunbury Mail on Wednesday.