Millionaire yachtsman Gordon Ketelbey, 64, climbs out of his car after plunging 30 metres down a cliff at Mosman

An author and yacht owner has escaped serious injury after his car plunged 30 metres down a steep embankment in Mosman, on Sydney's lower north shore.

Gordon Ketelbey, 64, who is an investor and also has a yacht (Zen) in the Sydney to Hobart Yacht Race, told police he was feeling dizzy and unwell before he lost control of his Toyota Landcruiser on Parriwi Road at 7.45am today.

He managed to climb out of the wreckage of the 4WD and walk to the top of the hill.

NSW Ambulance Inspector Michael Magyary told 9NEWS it was incredible.

"I'd say the seatbelt certainly did a lot of justice, and helped him out," he said.

"It's extremely lucky because this could have been a tragic accident."

Mr Ketelbey, who published The Invisible Entrepreneur, is currently in a stable condition at Royal North Shore Hospital.