Officers from the NSW Police Force’s crash investigation unit spent the afternoon at the scene of the crash, which involved a four-wheel drive and a B-double truck, and occurred at about 3.30am.

Lanes in both directions were closed while emergency service crews attended the scene, about 12km from Dubbo, with traffic diverted.

Police still haven’t officially released the names of the victims, a nine-year-old boy and his 12-year-old brother, however it is believed the siblings were from a Queensland family.

Another brother, aged just four, was airlifted to Westmead Childrens Hospital suffering severe internal injuries.

The parents, who were located in the front of the car, escaped without any major injuries although they were taken to hospital and treated for shock.

"All support is being offered to that family during this unfortunate tragedy," Orana Local Area Command duty officer Inspector Jason Pietruszka said.

The male truck driver, who was trapped inside his vehicle for an extended period of time, suffered serious injuries and after being treated at the scene was flown to a Sydney hospital.