A mother, 38, and her 13-year-old son were in critical condition after a semi-trailer ploughed into the back of their motor home late on Friday night. They are now in a stable condition, according to a spokeswoman from the Canberra Hospital.

Police allege a semi-trailer collided with the back of a Mitsubishi mobile home at Yarra, near Run O Waters at about 11pm on Friday. As a result, the motor home rolled and hit a tree. Police said the teenage boy was thrown from the vehicle.

He suffered serious head injuries in the accident.

The family was travelling south on the Hume Highway from their home in Newcastle when the incident occurred. 

The other family members were treated by NSW Ambulance Paramedics for injuries. The man was treated for shoulder pain while an 11-year-old boy was treated for minor injuries.

The driver of the truck, a 43-year-old man, was arrested and taken to Goulburn Hospital for mandatory blood and urine testing.

He was then charged at the Goulburn Police Station with two counts of dangerous driving occasioning grievous bodily harm, two counts of cause bodily harm by misconduct of a motor vehicle and negligent driving occasioning grievous bodily harm.

The truck driver was granted conditional bail and will appear in Goulburn Local Court on February 17.

A crime scene was established and was examined by forensic officers. One southbound land of the Hume Highway was closed following the crash but was reopened a short time later.

Anyone who witnessed the accident who has not yet spoken to police should call Crime Stoppers on 1800 333 000 or use the online reporting tool.