Police said the driver of the car, a woman aged in her 60s, is seriously injured and has been airlifted to Canberra Hospital.
They said the woman is believed to be in a critical condition. They did not specify where she was from.
The male truck driver was uninjured. He was taken to Goulburn Hospital for mandatory blood and urine tests.
Police said about eight cattle in the truck were killed in the accident or euthanised by Primary Industries personnel following the crash.
The crash scene is being examined by forensic specialists.
Police advise the road is expected to open within the hour.
A crime scene has been established.
The female motorist has been airlifted from the scene.
The Braidwood Road is closed at Tarago.
Kerrie Scarborough from the Loaded Dog Hotel said police had now closed the road near the hotel and were diverting traffic via Bungendore Road.
“The road has been closed right near the pub,” she said.
“Traffic is being diverted to the right on to the Bungendore Road and then onto the Mt Fairy Road.”
A female motorist is reported to be trapped with serious injuries following a collision near Tarago.
At about 12.50pm, emergency services and police responded an accident involving a car and a truck two kilometres south of Tarago.
Three NSW Ambulance road units and a rescue helicopter are on the scene.
There are also reports of numerous injured livestock.
The southbound traffic has been affected and motorists are advised to plan their trip accordingly.
Police are on site responding to the accident.
More to come.