As she fell beneath the wheels of a Sydney school bus, Ms Shin reached out an arm and pushed 11-month-old Meera away from the tyres that would have crushed the little girl to death.

"She died a hero," said Filippo Merenzi, who witnessed the tragedy as the bus turned left from Beecroft Rd into Hannah St close to Beecroft Primary School on Wednesday afternoon.

As distraught friends, neighbours and other mourners left bunches of brightly coloured flowers and handwritten notes on a pole near the corner where the accident happened, Mr Merenzi said he could not get the shocking image of the accident out of his mind. "She pushed the baby away from the tyre, it was incredible," Mr Merenzi said, trembling and with tears in his eyes.

Ms Shin, 38, was on her way to meet her 11-year-old daughter Kelly, who was arriving back from a three-day school camp at Tea Gardens on the mid-north NSW coast.

The white Port Stephens Coaches bus was carrying Kelly and 39 Year 6 Beecroft Primary School classmates as it stopped at the traffic lights at Beecroft Rd.

Carrying her baby on her hip, Ms Shin was hit as she crossed Hannah Rd. Police said it was still unclear whether the woman or the bus driver had the green light but inquiries were continuing.

Witnesses said they could see the accident unfold in slow motion, although it only took a split second.

"People were screaming and banging on the side of the bus yelling: Stop, stop, stop!" Mr Merenzi said.

"The driver didn't see her, the bus kept rolling until it went right over the top of her. She might have survived if it stopped after the impact."

Brides of Beecroft owner Wendy McGregor said she ran out from her shop.

"I heard a thump and the next minute I heard a beeping horn and everyone yelling: Stop!" Ms McGregor said.

"The baby was just screaming hysterically.

"I went out and I could see the woman under the bus and she was unconscious.

"I ran inside and asked my colleague to call triple-0 then I went back and checked her pulse and put her in the recovery position.

"She had tyre marks all over her stomach. She was unconscious, she had blue lips."

Ms Shin was lying between the front and rear wheels of the bus as teachers tried to shield the children on board from the horror - but Ms McGregor said that they all realised what had happened.

"The awful thing that's just haunting us is just the kids screaming on the bus. They were all upset," she said.

Witnesses said one woman cuddled the crying Meera before her older sister Kelly took over when she got off the bus.

One witness described the heartbreak of the 11-year-old girl cradling her crying sister in her arms.

Paramedics rushed Ms Shin to Royal North Shore Hospital but she died from her injuries soon after arriving. Meera was also taken to hospital and released into the care of her father yesterday morning.

Friends yesterday remembered Ms Shin as a loving mother who had been thrilled with the birth of her "little princess". "Haha yes harder with old age. Hehe but she is just so cute n lovely," she told a friend on her Facebook page.

The bus driver, a 69-year-old man from Port Stephens, returned a negative breath test after the accident but also underwent mandatory blood and urine tests.

The results were expected in a few weeks, police said.

Port Stephens Coaches spokesman Mark Newling said the driver had 40 years of experience driving buses and heavy vehicles.

"He was most distressed and jumped out of the bus when he realised what had happened and started doing CPR until the paramedics arrived," Mr Newling said.

"He did everything he could in the circumstances."

As the community rallied to help the grieving husband and children, a friend said the family was surrounded by loved ones inside their Beecroft home.

"It's a really difficult time for us at the moment and we want to grieve privately," friend Aida White said. "Both our girls are in the same Girl Guides unit.

"When I got home yesterday and heard what happened I gave my kids a big hug - you never know what's going to happen."

Laying a bouquet of flowers next to the road, Rayoung Kim said Ms Shin was one of her best friends, describing her as a wonderful person and wonderful mother.

"She was an absolutely beautiful lady," Ms Kim said.

In a card written in Korean and attached to the bouquet, Ms Kim wrote: "I was very happy with the time we had together. I hope you are well in another place."

Neighbours Carolyn McKenzie and her daughter Shelby left a bunch of flowers at the scene and another at the family's home: "It's devastating. It's the sort of community where everyone knows everyone," she said.

Ms McKenzie said Shelby went to school with Kelly last year and said she was well liked at Girl Guides.

"Kelly's mum must have been nice because Kelly was really nice," she said.

Staff and students at Beecroft Primary were visibly shaken by the tragedy, with the education department offering counselling during a special assembly yesterday.