UPDATE: A fire on the side of the Forrest Highway is now controlled with crews and police still on scene.
About 100 by 100 square metres of bushland was burnt near the Forrest Highway and Paris Road intersection, travelling north.
Police are on the scene to manage traffic and that side of the road was reduced to one lane.
The aerial attack have now returned to base and some of the 11 different fire vehicles have left the scene.
It is expected emergency service crews will monitor the scene for several hours.
The cause of the blaze is unknown, however the first report was of a car fire on the side of the highway.
EARLIER: One lane of the Forrest Highway, northbound has been blocked as firefighters work to extinguish a vehicle fire.
The Department of Fire and Emergency Services were called about the incident at 9.52am on Monday, December 24.
Eaton, Leschenault and Bunbury Fire Brigades are on the scene.
A helitanker has also been sent to the scene.
The fire is near the Paris Road and Forrest Highway intersection heading towards Mandurah.
Remember to slow down to 40km/hr when emergency service crews are working.
This year the state government introduced legislation to force drivers to slow down while emergency service crews are working to ensure their safety.