A car collided with a tree off the Kings Highway on Sunday.

The car was believed to be travelling west on the highway. It left the road near Mongarlowe at the top of Clyde Mountain between 5.30-6pm on February 12.

Emergency services attended the scene, but were unable to locate the driver as the car was empty.

The incident was not thought to be a fatality; however, police are still keen to locate and speak to the driver and/or passengers.

In an earlier serious incident on the weekend, three children and one man were taken to hospital after a crash on the highway.

The single-vehicle accident occurred near Braidwood, on the road to Batemans Bay, about 12.40pm on Saturday, February 11.

A 40-year-old man was airlifted from the scene to Batemans Bay Hospital and then on to Westmead Hospital in a critical but stable condition.

Two children, aged two and seven, were airlifted to the Children's Hospital at Westmead. Both children remain in a critical condition.

Another seven-year-old child with a head injury was airlifted from the scene to the Children's Hospital at Westmead.

The seven-year-old was accompanied by their mother, 40.

The Kings Highway was initially closed in both directions. Only one eastbound lane remained closed in the late afternoon, with all lanes reopened by 7pm.

If you have information about either incident, but especially the unknown driver of the Sunday incident, please contact police via Crime Stoppers.

The Crime Stoppers hotline is 1800 333 000, or go online to the website nsw.crimestoppers.com.au

All information provided by the public is received and treated in confidence.