Southbound traffic is at a standstill on the Pacific Highway at Nerong.

Two trucks collided at about 4.15 this morning, two kilometres north of Viney Creek Road, causing one to jack-knife.

NSW Fire & Rescue says the drivers were not injured.

Emergency services are still at the scene and a Hazmat Unit is on the way from Newcastle to clear diesel from the road.

There are no diversions in place and traffic is being held at the scene while the trucks are cleared from the road.

Traffic is back for 1.2 kilometres.