A truck has been engulfed by flames on the Hume Highway, causing traffic chaos for commuters.

Emergency services were called to the highway, near Bargo just after 2:30pm on Monday.

Fire fighters were confronted with plumes of smoke with the truck well alight, a Fire & Rescue NSW spokesperson said.

Drivers are urged to avoid the area with all southbound lanes closed near the Old Hume Highway. Traffic is backed up 6km.