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A Frenchman who tried to stop a deadly stabbing rampage at a Sydney mall has been promised an Australian visa.

Damien Guerot was labelled a hero after footage of him confronting knifeman Joel Cauchi with a bollard during Saturday's attack went viral.

Joel Cauchi killed six people and injured 12 others before he was shot dead by a police officer.

The attack in Bondi, which police say seems to have targeted women, has horrified the nation.

Amid the outpouring of grief around the country this week, there has also been a push to secure Mr Guerot - whose visa reportedly expires in a month - the right to stay in the country.

Prime Minister Anthony Albanese has said he will make sure Mr Guerot - who has been dubbed by some as "Bollard Man" - has no issue renewing his visa.

"I say this to Damian... you are welcome to stay for as long as you like," he said in a press conference on Tuesday.

"This is someone who we would welcome becoming an Australian citizen, although that would of course be a loss for France. We thank him for his extraordinary bravery."

The scene of Mr Guerot in a white T-shirt confronting Cauchi on an escalator has been broadcast around the globe. The video shows him wielding a plastic pole to ward him off.

Mr Guerot says he and a friend and fellow Frenchman, Silas Despreaux, both construction workers, had just launched into action without thinking - acting on pure adrenalin.

"We just saw him coming... we were thinking, 'We need to try to stop him'," Mr Guerot said in an interview with Australian TV network Channel Seven on Sunday.

Cauchi then turned and fled back down the escalator, with the pair in hot pursuit.

"We tried to maybe throw the bollard to him but we couldn't [get him]," Mr Guerot said.

Grabbing a chair, he sprinted after Cauchi on the next level down. At that point, a police officer was also on Cauchi's tail, and the men directed Inspector Amy Scott to her target. As he lunged at her with the knife, she shot him dead.

French President Emmanuel Macron praised Mr Guerot and Mr Despreaux as "true heroes" for their actions.

"Very great pride and recognition," he wrote on social media.

Police are now investigating how and why Cauchi, who is from the state of Queensland, committed such violence.

He had lived itinerantly for several years and was first diagnosed with a mental illness at 17, Queensland Police have said.

New South Wales Police on Monday said it seems "obvious" that he targeted women, who make up five of the six people killed.

The attack - at one of the country's biggest and most popular shopping centres - has shocked Australia, where mass killings are rare.

Flags across the nation have been lowered, the sails of the Opera house lit up in a tribute to the victims, and crowds of mourners have flocked to Bondi Junction to leaving flowers, teddy bears and cards.