UPDATE 5pm: A man in his fifties has died and another was airlifted to hospital after two cars collided head-on following a suspected road rage incident in Byford this afternoon.
Police believe two men in separate vehicles were involved in an incident shortly before 2pm.
One of the vehicles - a blue Great Wall - then drove off and shortly after smashed into a Nissan X-trail that was travelling in the opposition direction along South Western Highway.
The man in the X-trail died, while the 35-year-old driver in the other car had to be freed by emergency services and was airlifted to Royal Perth Hospital with leg injuries.
The 61-year-old driver who had been involved in the earlier altercation left the area and is now helping police with their inquiries.
Major crash are at the scene and have started making line markings in the gravel about 150-200m away from where the collision occurred.
The South West Highway was closed in both directions between Thomas Road and Larsen Road following the crash.