Two people have been airlifted to hospital after a serious crash in Waroona.
Police say a Mazda sedan travelling north on the South Western Highway collided head-on with a Nissan Patrol travelling south around 8.40pm on Saturday.
The Nissan then rolled.
The passenger in the Nissan, a 23-year-old woman, suffered serious injuries and was airlifted to Royal Perth Hospital.
The driver, a 27-year-old man, and three children under the age of six were taken to Peel Health Campus by ambulance.
They suffered non life-threatening injuries.
The driver of the Mazda, a 25-year-old woman, was also flown to hospital with non life-threatening injuries.