NSW Police investigate attacker who fatally stabbed six people at Sydney's Westfield Bondi Junction

Detectives are investigating the life and background of 40-year-old Joel Cauchi, who killed six people during a stabbing attack at a busy Sydney shopping centre.

NSW Police said the man from Queensland was shot dead by a senior police officer inside Westfield Bondi Junction on Saturday afternoon, after setting upon several people inside the complex with a knife and triggering an evacuation.

Six people were killed, including four women and one man who died inside the centre.

Another woman, named as Ashlee Good, died in hospital.

Two of the victims have no family in Australia and authorities are trying to contact their families.

Eight injured people, including a nine-month-old baby who has since undergone surgery, remain in Sydney hospitals after being rushed there by ambulance with some in a "serious but stable" condition.

Three other people presented to hospital for injuries overnight.

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Assistant Commissioner Anthony Cooke said Cauchi recently came to Sydney from Queensland and he had hired a "very small" storage facility, which investigating officers had now accessed.

"We have no information, we have received no evidence, we have recovered no intelligence that we have gathered that would suggest that this was driven by any particular motivation, ideology or otherwise," he said.

"We are continuing to work through the profiling of the offender but very clearly to us at this stage it would appear that this is related to the mental health of the individual involved."

Four patients are at St Vincent's Hospital. One woman is in ICU in a critical condition, one man is in ICU in a critical but stable condition, and two other women are in a stable condition.

A man and a woman are at Royal Prince Alfred Hospital. The woman is in a serious but stable condition in ICU, while the man is in a stable condition.

Three women are in a stable condition at Prince of Wales Hospital, one woman is in a stable condition at St George Hospital, one woman is in ICU in a serious but stable condition at Royal North Shore Hospital.

The child is in a critical but stable condition at Sydney Children's Hospital.

Warning: Some readers may find the following details of the attack, witness accounts and footage of the incident distressing.

Many shoppers sheltered in locked stores while scores of others ran to the closest exit of the shopping centre, one of the biggest in Sydney.

Witnesses have described panic and confusion inside the centre as the seriousness of the situation became clear.

The police officer who shot the offender, Inspector Amy Scott, is expected to be interviewed later on Sunday.

The Westfield was now a "very complex crime scene", according to NSW Police Commissioner Karen Webb.

It will remain closed on Sunday as authorities help with the removal of vehicles that remain in the car park.

Anyone with information about the attack, who witnessed it or had photos or video from the scene have been encouraged to contact local police.

Police investigating attacker

Assistant Commissioner Cooke said Cauchi was known to authorities and there were "elements" that indicate it was not a terror-related motive.

Police were combing through his background, home, vehicle and associates to learn more about the man, but say they do not believe he was targeting any specific victim or victims.

Witnesses say the first signs of trouble came when they saw shoppers running.

Videos from inside the centre show the knife-wielding man was confronted by others who tried to stop him as he moved between levels.

Several graphic videos show attempts to perform CPR on the injured, as an evacuation alarm echoes through the otherwise empty complex.

The Australian Federal Police (AFP) is also assisting state police with the investigation.

AFP Commissioner Reece Kershaw said it was too early to determine a motive and it would be "unhelpful to speculate".

Police inspector who shot attacker hailed a 'hero'

Prime Minister Anthony Albanese said the devastating scenes were beyond words or understanding for most Australians.

"This was a horrific act of violence indiscriminately targeted at innocent people going about an ordinary Saturday, doing their shopping," he said.

Albanese extended his deepest condolences to the families and loved ones of victims, while highlighting the courage and bravery on display at the scene.

"Staff for whom this should have been a normal shift, shoppers peacefully going about their lives, and yet for these Australians, their first instinct in the face of danger was to help someone else."

Commissioner Webb said the officer who shot the man dead was an inspector who had been "enormously courageous".

"She's doing well, under the circumstances," the commissioner said.

"She would need to be interviewed formally. So we just talked about that she's OK, her family is OK. She's got everything she needs for the time being."

Albanese said the senior officer was a "hero".

"There is no doubt that she saved lives through her action," he said.

"It is a reminder that those people who wear a uniform, are people who rush to danger, not away from it."

- This story was first published by ABC