At 4.30am, emergency services were called to the Princes Highway, Lake Tabourie, near Ulladulla, after reports that a crash had taken place.
The driver, a woman, and her two passengers – a man and a young child – died at the scene.
Police have yet to identify the bodies.
A fourth occupant of the car – a male passenger – was airlifted to hospital.
Police have established a crime scene which is continuing to be investigated to determine the cause of the crash.