Eight NSW Ambulance units and two helicopters were called to the crash site on Wilfred Barrett Dr at Magenta just after 11am, where it is understood two vehicles had collided head-on.

One of the critically injured patients has been transported by road to John Hunter Hospital, while the other two were transported by helicopter, an Ambulance spokesperson has said.

Meanwhile, in a separate incident, a man has been freed from a truck after a two-vehicle on Macquarie Street at Moira Park Road.

Police were called to the scene at around 11.11am, where they found a truck and a car had been involved in a crash.

The driver of the car, a woman in her mid-20s who suffered abdominal pain as a result of the crash, was conveyed to John Hunter Hospital.

The male truck driver was initially trapped by compression, and was later conveyed to hospital with suspected leg injuries.

A NSW Ambulance spokesperson said both patients were conscious, breathing and alert.

Traffic has since returned to normal in the area.