The 74-year-old - who murdered seven backpackers whose bodies were found in makeshift graves in NSW's Belanglo State Forest in the 1990s - has been transferred to the Prince of Wales Hospital in Randwick.

AAP understands he was transferred on Monday afternoon and is being held in a secure annex of the hospital where inmates are treated.

AAP understands Milat was called in for a diagnostic procedure and is expected to return to the Goulburn supermax jail in the coming days.

Milat was sentenced in 1996 to seven consecutive life sentences.

The former road worker also kidnapped British tourist Paul Onions but he managed to escape from Milat's vehicle.

Corrective Services commissioner Peter Severin said the community can rest assured transfers are done in the "most secure and safe way possible".

"We've got specialist teams to ensure that at any time there is absolute guarantee of safety and security," Mr Severin told Seven News.

High-risk and terrorism-related inmates are always guarded by specialist staff from the Extreme High-Security Escort Unit who control all movements and interactions, a NSW Corrective Services spokeswoman said.

"Extensive security planning and assessment is undertaken before such movements occur," the spokeswoman said in a statement on Tuesday.

Inmates are searched before they leave prison and when they return.

At least one form of restraint, handcuffs or ankle cuffs, stay on high-risk inmates during medical treatment, subject to medical requirements.

"These procedures ensure community safety and security," the spokeswoman said.

Australian Associated Press