Man-made hole found at NSW supermax jail

A cavity has been found during a search operation at Goulburn's maximum-security jail in NSW.

A cavity has been found during a search operation at Goulburn's maximum-security jail in NSW. (AAP)

Prison authorities have discovered a man-made cavity that's been dug inside a maximum-security jail in southern NSW.

Corrective services confirmed that a hole was found beneath a furniture workshop cabin at Goulburn Correctional Centre, a little more than 100 metres from the outside wall of the prison.

The cavity is about 60cm deep with an entrance of about 40cm by 18cm wide, and was discovered on Friday, authorities said.

The furniture workshop will remain closed to inmates until investigations into who made the cavity and its intended use are finalised.