Update (4.30pm): The fire is contained but not controlled.
So far the blaze has burnt 25 hectares of farmland.
Authorities intend to reopen the Old Bunbury Road within the next 15 minutes.
Several crews and the two bombers that were used to battle the blaze have been stood down.
A Department of Fire and Emergency Services spokeswoman said crews on the ground anticipate the fire will be contained within an hour.
Two water bombers have been called in to help battle a blaze that broken out in farming land near Old Bunbury Road and South Western Highway.
About 2.30pm on Friday, fire and rescue crews were called to a paddock on the western side of the road.
With strong north-westerly winds in the area, crews on the ground called for more resources to contain the fire.
About 3pm, the running fire jumped Old Bunbury Road and began heading towards South Western Highway.
A Department of Fire and Emergency Services spokeswoman said 13 fire appliances from across the region had converged to the scene to help battle the blaze.
She said at this stage, there was no threat to lives or homes.
A control point has been set up at a Bythewood property along Old Bunbury Road.
More as it comes to hand.
To keep up to date with the latest bushfire information visit the Emergency WA website.