The brave police officer who single-handedly stared down the man on a stabbing spree at a Sydney shopping centre and ended his murderous rampage has been hailed a hero.

Joel Cauchi entered the busy Bondi Junction Westfield shopping centre just after 3pm on Saturday armed with a large knife and began prowling through the complex.

The 40-year-old from Queensland terrorised crowds of shoppers enjoying a day out, stabbing at least 17, including a nine-month-old baby, and killing six.

Within minutes, as panicked shoppers ran towards the exits, a lone police officer entered the centre and ran in the opposite direction, towards the danger.

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A witness recounted hearing screams and people running before following Inspector Amy Scott upstairs as she pursued the knife man.

On level five, the two came face to face.

“As she continued to walk quickly behind him to catch up with him, he turned, faced her, raised a knife,” NSW Police Assistant Commissioner Tony Cooke said.

Scott, with a gun in hand, demanded Cauchi drop the knife but he did not comply.

“She discharged a firearm and that person is now deceased,” Cooke said.

She administered first aid to Cauchi after disarming him.

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The witness said Cauchi would have kept going, if not for the officer.

“He had a nice big blade on him so she chucked the knife away … it looked like he was on a killing spree,” the witness told ABC News.

Police Commissioner Karen Webb hailed the “enormously courageous” actions of Senior Inspector Scott and said she was doing well under the circumstances.

“The actions of Inspector Amy Scott had no doubt prevented the loss of additional lives,” Webb said on Sunday.

Premier Chris Minns said Scott’s “instinctive bravery” as she ran towards danger “without a shadow of the doubt saved many, many lives”.

“Running towards the danger (she) exemplified the very best of public service in this state,” Minns said on Sunday.

“This state owes her an enormous debt of gratitude.

“There are many committees to run through before someone’s actually given a hero award or a bravery award, but I think we can call it – this is outstanding courage and bravery under incredibly difficult circumstances.”

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Prime Minister Anthony Albanese described Scott as a hero who “no doubt saved lives through her actions”.

“We give thanks to our police and emergency services – the wonderful inspector who ran into danger by herself and removed the threat … without thinking about the risk to herself,” he said on Sunday.

“That bravery was quite extraordinary that we saw yesterday the best of Australians amidst this extraordinary tragedy.”

-AAP