After a series of hunger strikes in prison over the past decade, it is understood the 74-year-old is suffering health problems due to his extreme weight loss.
A spokeswoman for NSW Corrective Services could not confirm what procedure the killer was undergoing at the hospital for privacy reasons.
However, a source close to the Milat family told ABC that the murderer recently lost 20 kilograms and was currently being assessed for possible organ failure linked to geriatric anorexia.
It is understood he was transferred to the Prince of Wales Hospital in Randwick on Monday afternoon and is being held in a secure annex of the hospital where inmates are treated.
It’s believed that he is expected to return to the Goulburn Supermax jail in the coming days.
Milat has previously needed hospital treatment while in prison.
In 2001, Milat had injured himself swallowing metal objects, including razors and staples, while in 2009, he cut off his pinky finger with a plastic knife, supposedly with the intention of posting it to the High Court.
He was transferred, under high-security, to Goulburn Hospital, where doctors determined the finger could not be surgically reattached.
In 2011, in a dramatic attempt to be given a PlayStation, the murderer lost 25 kilos on a hunger strike.
The 74-year-old, who murdered seven backpackers whose bodies were found in makeshift graves in NSW’s Belanglo State Forest in the 1990s, 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 NSW Commissioner Peter Severin told the Seven Network the community could rest assured transfers were done in the “most secure and safe way possible”.
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 Corrective Services NSW 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, she said. 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.