Teen critically injured after driver hits tree 'avoiding wombat'

A teenage boy has been critically injured after being thrown from a car after the driver swerved to avoid a wombat and smashed into a tree.

An off-duty nurse was the first on the scene after a driver veered off the Illawarra Highway at Burrawang, in the Southern Highlands, about 11.30pm last night.

The boy was ejected from the sedan and suffered serious head injuries.

The local Rural Fire Service helped the nurse treat the boy until paramedics arrived.

The teenage boy was then airlifted to The Royal Children’s Hospital at Westmead in a critical but stable condition.

9NEWS has contacted the hospital about his condition.

READ MORE: Man dies swerving to avoid kangaroo

The driver was taken to Liverpool Hospital while two other passengers were treated on the scene.

The crash unit is investigating and has appealed for witnesses or anyone with dashcam of the incident to come forward.

This comes after a man was killed when he rolled his ute after swerving to avoid a kangaroo south of Bingara.