Police call for witnesses after SW crash closes highway

South Western Highway was closed for two hours on Sunday after a head on crash in North Boyanup.

At about 11.30am, a Mazda utility driving north on South Western Highway crossed to the other side of the road and collided head on with a Nissan utility.

As a result of the collision the Mazda was sent off the road and hit a tree.

The 68-year-old female driver of the Mazda sustained serious injuries and was cut from the vehicle by Department of Fire and Emergency Service personnel.

She was flown to Royal Perth Hospital by the RAC Rescue Helicopter.

Four people were in the Nissan at the time of the crash, with the male driver sustaining leg injuries and a female passenger receiving non-life-threatening injuries.

Both were taken to Bunbury Hospital.

The other two passengers were not injured.

Police are investigating and would like to speak to anyone who witnessed the crash or saw the vehicles driving prior to it.

Any witnesses are asked to call Crime Stoppers on 1800 333 000 or make report online at crimestopperswa.com.au