Attacker identified in Sydney mall stabbing that killed 6

Australian police on Sunday said a 40-year-old itinerant with mental illness was behind a Sydney shopping centre stabbing rampage that killed six people, including a new mum whose nine-month-old baby is still in hospital with serious wounds.

New South Wales police Assistant Commissioner Anthony Cooke said the assailant -- who was shot dead by a senior police officer at the scene on Saturday -- was Queensland man Joel Cauchi.

Five women and one male security guard were killed in the attack as Cauchi roved through a packed shopping centre in the city's Bondi Junction neighbourhood with a large knife. Twelve more people are still in hospital.

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"The sound of people screaming was horrific," said eyewitness Daphi Kiselstein, who was shopping at the time of the attack and took refuge in a store with other terrified people.

Cooke said there was no evidence to suggest Cauchi was "driven by any particular motivation, ideology or otherwise."

"We know that the offender in the matter suffered from, suffers from, mental health," he added.

Cauchi was tracked down and shot dead by solo senior police officer Amy Scott, who was instantly hailed by Australia's prime minister as a "hero" who had saved countless lives.

Cauchi's parents said their son had been living in a vehicle and hostels of late, and was only in sporadic contact via text messages.

Police said he was diagnosed with a mental health issue at age 17, but they had no indication about why he may have become violent.

His parents issued a statement through police offering condolences to their son's victims and their families.

They had also sent a message of "support" to the officer who shot him dead, "expressing their concerns for her welfare."

Queensland police said Cauchi had been in contact with police several times over the last four to five years but has never been arrested or charged with any offence.

He is believed to have travelled to Sydney about a month ago and hired a small storage unit in the city. It contained personal belongings, including a boogie board.

The attack has caused sorrow, outrage and shock in Sydney, where residents are relatively unaccustomed to violent crime.

The shopping centre is the focal point of a well frequented suburb near the famed beach, and is always filled with shoppers and families going for meals or to the cinema.

Among the victims was 38-year-old mother Ashlee Good, who succumbed to her injuries after desperately passing her baby to two strangers in the hope they could save the child's life.

Good's family described her as "a beautiful mother, daughter, sister, partner, friend, all round outstanding human and so much more".

"To the two men who held and cared for our baby when Ashlee could not -- words cannot express our gratitude", they said in a statement to Australian media.

The baby, named Harriet, was said to be recovering well after lengthy surgery.

Two of the victims are said to have no family in Australia and attempts are being made to contact relatives overseas.

A Facebook profile said Cauchi came from Toowoomba, near Brisbane, and had attended a local high school and university.

A distinctive grey, red and yellow dragon tattoo on his right arm was used to help identify him.

Prime Minister Anthony Albanese said Australians were struggling to understand an "unspeakable" attack that is "really just beyond comprehension".