A NSW Police Media spokesperson said the truck hit a parked car that appeared to have no people inside.

The truck caught alight and the driver appeared to have suffered some injuries to their legs.

The driver, breathing and conscious, was taken to Singleton hospital before  Westpac Rescue Helicopter transferred the patient, a male believed to be late 50s, suffering multiple injuries, to John Hunter Hospital.

Some grass near the truck caught alight and NSW Rural Fire Service was called to assist.

The New England Highway was closed in both directions.

Motorists are advised to avoid the area and expect delays.

Eastbound light vehicles are being diverted via Thomas Mitchell Drive, then Denman Road and onto the Golden Highway.

Westbound light vehicles are being diverted into Lemington Road to Golden Highway, then Denman Road into Muswellbrook.

Heavy vehicles in both directions should use the Golden Highway.

According to Live Traffic NSW, heavy vehicles including B-doubles can access Bayswater Power Station and Liddell Power Station from the Newcastle side of the accident scene via the Golden Highway, Denman Road, Thomas Mitchell Drive, onto New England Highway, to head east to the power stations.