Police said the truck, which was carrying a tile bonding agent, was about 500m south of the Yass Service Centre on the highway when it caught fire about 2.40am.

The driver escaped without injury.

Police and NSW Fire and Rescue closed the highway in a southbound direction while the fire was brought under control.

At 8am, the RTA Live Traffic website was reporting one southbound lane had been reopened, and traffic conditions in the area were light. Police had departed the scene.