Ivan Milat, Australia's most notorious serial killer who was serving seven life sentences for the murders of seven backpackers, has died aged 74.

Key points: Milat was arrested in 1994 after a massive police investigation

Milat was arrested in 1994 after a massive police investigation His victims' bodies were discovered in the Belanglo State Forest in 1992 and 1993

His victims' bodies were discovered in the Belanglo State Forest in 1992 and 1993 Despite overwhelming evidence, he claimed he had nothing to do with the murders

Milat was diagnosed with terminal oesophagus and stomach cancer in May.

He had been transferred for advanced pain relief treatment to Sydney's Prince of Wales Hospital on October 11.

He died in the medical wing of Long Bay jail this morning.

Milat had been treated at the same hospital earlier this year after being moved from Goulburn Supermax jail, where he had been in solitary confinement.

In a statement, the NSW Department of Corrective Services said Milat died 4.07am.

His body will now be transferred to the Coroner, who investigates all deaths in custody.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 52 seconds 52 s Ivan Milat's body is taken from Long Bay jail.

NSW Corrections Minister Anthony Roberts said he was glad Milat was dead.

"He can rot in hell," Mr Roberts said.

"He showed no remorse.

"He was sentenced to remain in jail for life, that sentence was carried out and he died in jail."

Milat was arrested in 1994 following one of the biggest police investigations in Australian history, after seven bodies were discovered in shallow graves in the Belanglo State Forest, south-west of Sydney, between 1992 and 1993.

His victims were all hitchhikers travelling south along the Hume Highway near Liverpool in western Sydney, who disappeared between 1989 and 1992.

They were Deborah Everist and James Gibson, both 19, from Victoria, Simone Schmidl, 21, from Germany, Anja Habschied, 20, and Gabor Neugebauer, 21, a couple also from Germany, and Caroline Clarke, 21, and Joanne Walters, 22, from Britain.

Two of the victims had been shot multiple times in the head, as if used for target practice. One had been decapitated. Three had stab wounds that would have caused paralysis and two of those victims had their spinal cords completely severed.

Court documents state that all but one of the victims had been subjected to "sexual interference, either before or after death".

Milat, who was convicted in 1996, never admitted to the murders.

Milat spent his final days in Sydney's Long Bay jail hospital. ( Supplied: NSW Corrective Services )

A life of brutality

Ivan Robert Marko Milat was born on December 27, 1944 in Guildford, western Sydney, to a Croatian father, Steven, and an Australian mother, Margaret.

He was the fifth of 14 children, brought up in a brutally violent, financially strapped home.

The Milat boys were keen hunters and gun enthusiasts, and were frequently in trouble with police.

By age 17, Milat had been sent to juvenile detention for six months on burglary charges, beginning an adulthood in and out of prison for various theft offences.

Charges against him took a more sinister turn in 1971, when he was accused of abducting two 18-year-old female hitchhikers, threatening them at knifepoint and raping one of them before they escaped.

He was acquitted in 1974, however, after his lawyer, John Marsden, discredited the women by accusing them of being lesbians, such were the prejudices of the time.

Ivan Milat was convicted in 1996 and has never shown remorse for his crimes. ( AAP )

When not in jail, Milat had worked for the Roads and Traffic Authority out of Liverpool but travelled all over the state.

In 1990, he picked up British hitchhiker Paul Onions, then aged 24, in Casula, near Liverpool, introducing himself as "Bill".

Mr Onions managed to escape after Milat pulled a gun on him and was rescued by a passing car and taken to a police station.

Remarkably, Onions' account was not followed up by police at the time.

After a widespread appeal for information following the discovery of the bodies in the forest, Mr Onions again contacted police and was flown back to Sydney in 1994, where he identified a photo of Milat — by then of interest to police due to other tip-offs — as "Bill".

A few weeks after Mr Onions' identification, police raided Milat's home to find multiple incriminating items, including clothing, camping equipment and other possessions belonging to the dead backpackers, and various weapons and ammunition.

Milat was found guilty in July 1996 of the murders of the seven backpackers and of the abduction of Mr Onions.

He was also linked to unsolved missing person cases, including the disappearance of three women, Leanne Goodall, 20, Robyn Hickie, 18, and Amanda Robinson, 14, in the Newcastle region in the late 1970s, where he was working on the roads at the time.

Milat was briefly married in the 1980s but divorced amid claims of domestic violence.

He has one daughter, Lynise, from an affair with the wife of his brother, Boris.