LATEST: The fire 10 kilometres south of Gunning is now under control.
A fire is burning out of control near the Mundoonan rest area, north of Yass.
One southbound lane of the Hume Highway is closed and traffic is banked up, with no alternate route available.
The Roads and Maritime Services (formerly RTA) advised that heavy traffic in the area and motorists should expect significant delays.
Emergency vehicles are on the scene and the Rural Fire Service is working to get the one-hectare blaze under control.