Police dogs and a surveillance plane were called in to hunt up to three men who fled the scene of a serious crash on the Kwinana Freeway last night.
The crash happened about 200 metres south of Thomas Road in Bertram.
Up to five men were travelling south in a 4wd when it rolled at least three times in the south-bound lane, coming to a rest on its roof propped against a pole. One man was thrown from the car from the force of the impact, and was rushed to Royal Perth Hospital with suspected head and spine injuries. He remained in a stable condition last night.
Another man, believed to be a passenger, was taken to Rockingham Hospital with non-life threatening injuries.
Passing motorists stopped to give assistance to the men while waiting for emergency services to arrive.
Two young men, who asked not to be named, said they helped remove a passenger from the back seat of the vehicle.
Another young couple on their way to Margret River gave assistance to the man thrown out of the car and onto the grassed strip on the side of the freeway.
Don Phillips, 63, said he was passed by the vehicle a few kilometres back from the crash site.
"He came screaming up behind me flashing his lights at me trying to get me off the road," Mr Phillips said.
One of the passengers was standing up with more than half his body hanging out the window, yelling and gave him the finger, Mr Phillips said.
The man didn't seem to be wearing a seatbelt, he said.
When he came upon the crash site, Mr Phillips, who has first aid training, prevented people from moving the man lying on the ground before ambulance officers arrived.
The police airwing - polair - was last night sweeping the area trying to find up to three men who are believed to have fled the scene.
Kwinana Freeway after Thomas Road was closed for more than five hours last night as major crash officers investigated the scene.
Police were investigating if both speed and alcohol were a factor in the crash, Senior Constable Graham Daisley said.