Emergency services were called to the accident near the intersection of the highway and Tumbarumba Road at Alfredtown about 4.20pm on Sunday.

Both occupants of the car, an elderly man and woman, had to be freed from the wreckage by rescue crews.

They were taken to Wagga Base Hospital but police have since confirmed the man and woman have died.

They are yet to be formally identified.

The truck driver wasn't injured but was taken to hospital to undergo mandatory blood tests.

Officers from the Riverina Police District have established a crime scene and are investigating the circumstances surrounding the crash.

A report will be prepared for the coroner.

Earlier, a NSW Ambulance spokesman said the man and woman, both believed to be aged in their 70s or 80s, were unconscious when paramedics arrived at the scene.

The spokesman said both of them sustained serious head injuries and had been in critical conditions.

A Canberra-based ambulance rescue helicopter was dispatched to the scene but was later diverted to the hospital.

Fire and Rescue NSW firefighters, including a hazardous materials crew, were also on the scene.

It is understood the truck involved in the crash was leaking fuel onto the road.

Police, the Wagga Volunteer Rescue Association and NSW Rural Fire Service volunteers were also in attendance.

The crash has closed the Sturt Highway in both directions and there are significant delays in the area.

Traffic in both directions is being diverted via Tumbarumba Road, Gregadoo East Road and Elizabeth Avenue to rejoin the highway.

The diversion is suitable for all vehicles.