In the midst of a Sydney mall stabbing rampage, witnesses say a fatally wounded mother handed over her injured nine-month-old baby to a stranger to save the infant's life.

Stories of courage are still emerging from Saturday's attack, in which a 40-year-old knifeman with mental illness roamed the packed shopping centre, killing six people and seriously wounding a dozen others.

Lone senior police officer Amy Scott is being hailed for tracking down, and then shooting dead the assailant during his killing spree.

One young man was filmed fending off the attacker on an escalator, armed only with a shopping centre bollard.

Storekeepers opened their doors to shelter frightened shoppers.

But the harrowing story of 38-year-old mother Ashlee Good's desperate final act to save her baby daughter Harriet has struck a chord with many shocked Australians.

Witnesses told local media she was heard screaming when the assailant approached her in the shopping complex.

"The baby got stabbed," one man at the scene with his brother told Channel 9 News in the aftermath of the attack.

"The mum got stabbed and the mum came over with the baby and threw it at me," he said.

Within hours of the attack, police said the toll had climbed to six after Good died in hospital.

Her baby is still in "a serious but stable condition" in hospital, New South Wales police assistant commissioner Anthony Cooke said Sunday.

In a statement to Australian media, 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" the statement said.

The child, they said, was "doing well" after "hours of surgery".

Sky News Australia television reporter Laura Jayes was near tears as she revealed on air that she knew the sixth victim, who she described as an "incredible athlete".

"I can tell you that it was a mother, a mother in the prime of her life, a new mother with a nine-month-old baby," Jayes said.

"I can't imagine her needing to hand over the most precious thing in her life."

"Her baby went to surgery and her mum didn't make it. So that's really hard news to take. And I am bringing you that not knowing about the other five victims. But there's one victim I do know about. And it's just so cruel."

Prime Minister Anthony Albanese praised the courage displayed by "ordinary Australians" in the attack.

- 'In harm's way' -

"We also see the footage of ordinary Australians putting themselves in harm's way in order to help their fellow citizens," he told reporters Sunday.

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

One short video widely circulated on Australian media showed a young man in a white T-shirt fending off the attacker on an escalator, armed only with a bollard. It did not show how the confrontation ended.

Many people praised shopkeepers who gave them shelter in the midst of the rampage.

Albanese singled out the "wonderful" police inspector -- named in local media as Amy Scott -- who shot and killed the offender.

She "ran into danger by herself and removed the threat that was there to others without thinking about the risks to herself", the prime minister said.

An unidentified middle-aged witness at the scene told national broadcaster ABC he saw the shooting.

"All I heard was 'put it down'. And then she shot him," he said.

"If she didn't shoot him, well he would have kept going. He was on the rampage. He was on the bloody rampage. And then she walked over and was giving him CPR."

Police said the senior officer was near the shopping centre when the stabbing unfolded and was guided to the gunman's location by people there.

"She took the actions that she did, saving a range of people's lives," said New South Wales police assistant commissioner Anthony Cooke.

"She was on her own."