The 10-year-old girl was rushed to the Children's Hospital at Westmead for treatment after the car she was travelling in collided with a semi-trailer at the intersection of Gocup Road and Snowy Mountains Highway.

The girl's mother remains in a critical but stable condition in Canberra Hospital, while her four-year-old fellow passenger is in a serious but stable condition at Westmead.

Earlier: A PREGNANT woman's unborn baby has died after their vehicle collided with a truck in the Snowy Valleys at the weekend.

The woman's two daughters also remain in a critical condition with one unlikely to survive.

About 3pm on Saturday, a Subaru Liberty travelling along Gocup Road failed to give way to a semi-trailer while turning onto the Snowy Mountains Highway, causing the two vehicles to collide.

The 29-year-old woman from Nichols, ACT, driving the vehicle, alongside her 10-year-old daughter and 4-year-old daughter, were freed by emergency services.

The mother, who was 30 weeks' pregnant, was airlifted to Canberra Hospital and the children transported to Westmead Children's Hospital, all in a critical condition. Her baby didn't survive.

The 10-year-old daughter remains in a critical condition, and Riverina Police District Inspector John Aichinger said the prognosis was not good

"Injuries to the 10-year-old are sadly not good, and the likelihood of her surviving is not fantastic at this point in time," he said.

The 4-year-old also remains in a critical condition.

The 58-year-old male truck driver was not injured in the collision, and police say he is assisting with inquiries, and a crime scene was established a processed by the Crash Investigation Unit.

Snowy Valleys mayor James Hayes said the news of the crash was "tragic".

"It's just awful, we haven't been able to get any positive resolution on such a dangerous intersection despite constantly working with our local member to see it change," he said.

Cr Hayes said the death, and many others which come before it, hit many of the residents of the region close to home.

"We live in a beautiful part of the country but the fact is there's danger out their on the roads and we need to be vigilant, but we also expect those in authority to do the same and do the best they can to keep it safe," he said.

In 2015, the state government pledged $70 million to upgrade Gocup Road, but Cr Hayes said the works "didn't do anything".

"It just created a big highway that ends in a bottle neck with a difficult intersection still there," he said.

"It needs rumble strips, it needs alternatives and all of our requests for this have fallen on deaf ears because the unfortunate thing is you need to become a black spot on the map for things to change."

Transport NSW has recorded a total of three fatalities on Gocup road between 2014 and 2018, plus a further person seriously injured. At the intersection of Gocup Road and Snowy Mountains Highway, there were an additional two serious injuries and two moderate injuries for the same period.

"It's not our road, but it's our people," Cr Hayes said.