Australia's most notorious serial killer Ivan Milat has been admitted to a Sydney public hospital for medical treatment.

Corrective Services Commissioner, Peter Severin confirmed to 7NEWS a 74-year-old inmate was taken from Goulburn's Super Max prison to Prince of Wales Hospital, in Sydney's eastern suburbs.

Milat, who murdered seven backpackers, is being treated for what is understood to be a worsening, age-related condition. 7NEWS understands that Milat has had visits from many specialists recently and some are wondering if he will return to supermax.

Milat will have two guards on him 24 hours per day.

In the darkness, a high-security convoy made the 200 kilometre, two-hour journey on Monday night to bring Milat to hospital.

Severin said the high-risk prisoner is located in a secure ward and is being jointly treated by staff from the department of corrective services and NSW Health.

"We've made very strong security arrangements for that, we've got specialist teams to ensure that at any time there is absolute guarantee of safety and security, both in the context of the person but also the context of the environment that the person has to be in for a period of time," Severin said.

Chevron Right Icon 'We've got specialist teams to ensure that at any time there is absolute guarantee of safety and security.'

"You can be rest assured it is done in the most secure and safe way possible."

The government wasn't even aware Milat had been moved until informed by 7NEWS.

Milat, who was convicted of the 1990s NSW backpacker murders, has been serving consecutive life sentences in Goulburn Correctional Centre's SuperMax wing for the past two decades.

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In October 2017, NSW Supreme Court justice Megan Latham dismissed his latest bid for a review, noting points raised had already been considered in previous applications.

Between 1989 and 1992, several backpackers went missing outside Sydney, leading to a widescale scouring of bushland in the Belanglo State Forest.

The search recovered the bodies of seven dead male and female travellers, of Australian, British and German backgrounds.

A police vehicle stops access the area, where investigators are searching for evidence after the discovery of bones and a skull in Belanglo State Forest in 2010. Credit: Miles Godfrey / AAP

Investigators believed the deaths were connected due to similarities at some of the crime scenes but it took British backpacker Paul Onions - forced to run from Milat after being picked up while hitchhiking in 1990 - to link his moustachioed attacker to the area in 1994.

British backpacker Paul Onions, left, is escorted into court by an unidentified man, in 1996 in Sydney Australia. Credit: Rick Rycroft / AP

This allowed police to finally raid Milat's property and after 15 weeks of trial, he was found guilty in July 1996 and handed seven life sentences plus an extra six years for the Onions attack.

Throughout his stay at the hospital, Milat will be under constant restraint with two guards always by his side.