The police spokesman said the woman died at the scene and the man was taken to hospital with serious injuries.

"The male rider was airlifted to Perth by the Royal Flying Doctor Service," he said.

"The man and woman are known to each other."

Anyone who saw the incident or has dash cam footage or CCTV from the area around the time of the crash is asked to contact Crime Stoppers on 1800 333 000 or report online at crimestoppperswa.com.au.