At about 8.15pm on Wednesday, emergency services were called to the intersection at Sturt Highway and McNickle Road in Ashmont, for a car and truck collision.

Police have begun their investigations into what caused the incident that saw the highway is closed in an eastbound direction.

A 19-year-old male remains in a critical, but stable, condition at St George Hospital after sustaining serious head injuries.

Riverina Police District Acting Inspector Geoff Gray said the crash occurred outside the Silvalite Fuel Station.

"It's believed a Toyota Yarris [driven by the 19-year-old man] was driving south on McNickle Road and collided with a semi-trailer, fully loaded with livestock," he said.

"The cause is still under investigation and the drivers are yet to be interviewed. The truck driver [a 54-year-old man] was taken to Wagga Base hospital for blood and urine testing, but we are still waiting for results."

A NSW Police spokesperson said the passenger of the car, a 19-year-old woman, suffered minor injuries and underwent treatment at Wagga Base Hospital.

The spokesperson said the driver of the truck was not injured.

A Murrumbidgee Local Health District spokesperson said the 19-year-old male was airlifted by NSW Air Ambulance to St George Hospital in Sydney at about 12.30am on Thursday.

Multiple fire trucks, at least two ambulances and the Wagga Rescue Squad attended the scene in Ashmont to divert traffic and assist those in the vehicles.

Acting Inspector Gray said incidents such as this are always tough for the emergency services to attend.

"Sometimes there are local people and it is never an easy job," he said.

Acting Inspector Gray said this crash, along with one in Tarcutta on Thursday morning, are a timely reminder for Wagga residents to be safe on the roads and drive to the conditions.

"Fatigue is always an issue," he said.

"Drivers are reminded to have adequate rest breaks."

Officers from the Riverina Police District are investigating the circumstances surrounding the crash.

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