A truck driver was airlifted to Canberra Hospital in a critical condition after a two-vehicle collision on the Monaro Highway on Friday.
The truck collided with a ute towing a caravan on the highway 20 kilometres north of Cooma about 11am.
The driver, a 27-year-old man, suffered suspected fractures to his legs and pelvis after the truck rolled onto its side as a result of the collision.
He was trapped in the vehicle and had to be rescued by SES crews.
"This is a very serious accident that has occurred on the Monaro Highway," acting inspector Ben Bowles said.
"We urge drivers to exercise caution of our roads, particularly on the Monaro Highway, which sees an increase in traffic at this time of year with commuters to the alpine areas.
"We obviously have had some very serious accidents occurring on the highway this year resulting in the deaths of persons."
The caravan was destroyed in the incident, and both the ute and the truck sustained extensive damage.
Four other people were treated at the scene for minor injuries but were not taken to hospital for treatment. The driver of the ute was taken to Cooma Hospital for mandatory blood and alcohol testing.
Police established a crime scene at the site of the collision.
Crash investigation crews are still determining the circumstances that led to it and no arrests had been made as of Friday evening.
The Monaro Highway's northbound lanes were closed for several hours as a result of the incident, causing long traffic delays.
Emergency services remained at the scene late into the afternoon, but the site had been cleared by 5.30pm.
Police are urging anyone who witnessed the incident, or who may have dashcam footage of it, to contact Crime Stoppers on 1800 333 000.
One person died in a crash on the Monaro Highway on September 3 after a truck collided with a car near the Royalla solar farm.