A 4,000-year-old Aboriginal rock art site has been found deep in rugged bushland in the Wollemi National Park, north-west of Sydney.

It is being described as one of the most significant finds in half a century.

New South Wales Premier Bob Carr has told Parliament that more than 200 separate pictures in pristine condition have been discovered in a cave in Wollemi.

Mr Carr says it is a major find that will shed more light on the history of Aboriginal people in the Sydney basin.

"These illustrations are for the most part 4,000 years old," Mr Carr said.

The rock art comprises up to 12 different layers, created over time.

The images depict both human and animal figures, some half-and-half.

There are drawings of birds, lizards and also a wombat, said to be rarely found in rock art.

A team of experts has made a detailed assessment of the site, the location of which is being kept secret in order to protect it from vandals.