Earlier: Multiple fire crews are responding to a bushfire near the Hume Highway just north of Marulan.
The fire started just before 12.25pm on Saturday, and is currently at a 'watch and act' level.
The blaze has caused long delays for motorists, with the highway closed in both directions at Inverary Road.
Smoke is also impacting on road conditions for drivers.
An RFS spokesman said 32 firefighters and nine fire trucks are currently on the scene.
"We are also looking to send an aircraft to assist ground crews," the spokesman said.
The fire is currently heading in an easterly direction, with up to five houses being in close proximity to the blaze.
The spokesman said while the fire currently isn't causing a direct threat to homes, people living in the area should be monitoring conditions.
Fire crews are currently working on parts of the Hume Highway to control the blaze.
"We are asking people to keep an eye on the NSW Live Traffic site for further updates," the RFS spokesman said.