Truck carrying petrol and diesel catches fire, resulting in extensive delays and major clean-up operation on Monaro Highway

The B-double fuel tanker caught fire on the Monaro Highway overnight. (ABC News: Tobias Hunt )

A large clean-up operation is underway on the Monaro Highway after a truck carrying diesel and petroleum burst into flames overnight.

Emergency services attended a call out to a vehicle fire about 1:00am, where they found the B-double fuel tanker alight just south of Williamsdale in southern NSW.

The driver of the truck escaped uninjured but was treated by paramedics for smoke inhalation at the scene.

An extensive clean-up operation is underway on the highway, with delays and alternative traffic conditions in place.

Superintendent Glenn Brewer from ACT Fire and Rescue said the truck fire had caused significant damage to the highway.

"We are trying to let as much traffic through as we possibly can, but given the conditions, the burnt-out vehicle is still on the side of the road and has caused some quite significant damage to the road pavement as well," he said.

The truck was carrrying 48,000 litres of petrol and diesel when the blaze took hold. (ABC News: Tobias Hunt)

All heavy vehicles are being stopped at the exit to Royalla.

Authorities are currently unsure how the fire started, but do not believe it was suspicious.