A Canberra-bound section of the Federal Highway was closed after a truck caught fire two kilometres south of Collector on Thursday morning.
Fire crews are attending the fire which was reported about 8.10am, and significant delays are expected.
NSW Rural Fire Service spokesman said the burning semi-trailer's prime mover caught alight and crews were working to isolate the fire.
"It is contained to the pime mover now, but the crews have a bit of salvage work to do whist they pump out the left over fuel in the truck's fuel tanks," he said.
Police said the fire has caused major damage to the prime mover, which was carrying a full load of steel, but the male driver of the semi-trailer escaped injury.
Vehicles are moving slowly past the incident but one of the two southbound lanes remains closed.
Bumper to bumper traffic was queued 1.5 kilometres back as of 9.20am on Thursday.
Visibility is limited in the area due to fog so drivers are being encouraged to slow down or avoid the area.
More to come.