Sydney police on Sunday ruled out terror or ideology as a motive after a man killed six people in a random stabbing attack on Saturday in one of the city's busiest shopping centres.

Police were called to the Westfield Bondi Junction mall in the city's east just before 4 pm on Saturday after the stabbing reports.

Witnesses described how the man, who was identified by police as Joel Cauchi on Sunday, wore shorts and an Australian national rugby league jersey. He was seen running through the mall with a knife randomly attacking people. Some shoppers and staff at the mall tried to stop him and crowds sheltered in shuttered shops.

"We have seen the footage of ordinary Australians putting themselves in harm's way to help their fellow citizens. That bravery was quite extraordinary ... it's the best of Australians amidst this tragedy," Prime Minister Anthony Albanese said on Sunday.

The 40-year-old assailant fatally knifed six people and injured at least 12 before he was shot dead by a senior female police officer who confronted him, it was reported.

"This was a terrible scene," Assistant Commissioner Anthony Cooke told a media conference Sunday, who confirmed the man was known to police in Queensland.

"There is still to this point, nothing that we have, no information we received, no evidence we have recovered or intelligence that we have gathered that would suggest that this was driven by any particular motivation, ideology or otherwise."

Cooke said it had been determined Cauchi had suffered mental health issues in the past and police had spoken to his family after the attack.

Five of the six victims killed were women, and several people including a nine-month-old baby were taken to hospital with stab wounds, police said on Saturday. The baby was in a serious but stable condition, police said.

The mother of the baby was reported by local media as having died in hospital from her injuries.

"Our hearts go out to the families and loved ones of those who have been so brutally killed during such a senseless attack," a statement from King Charles about the attacks said on the Royal Family's X account.

Australia, a country of about 26 million people, has some of the world's toughest gun and knife laws, and attacks such as the one on Saturday are rare.