Elderly NSW man missing on farm

An 85-year-old man has gone missing on a 400-hectare property on Sydney's outskirts.

The elderly man, who has dementia and bad eyesight, has lived at the religious retreat, near Camden, for 20 years, but disappeared on Thursday afternoon, police said.

He had driven a ute to unlock a gate on the property but didn't return.

The vehicle has been found bogged on a track on the farm, which is bordered by the Nepean River and Hume Highway.