A toddler has died after being hit by a car while walking on a footpath in Sydney's west.

Paramedics were called to Marion Street in Auburn just after 9:30am to treat the one-year-old child and his great grandmother.

The woman was walking with the toddler along the footpath when they were struck by a Toyota sedan

Police said the car was driven by a woman aged in her 50s to 60s who was also a P-plater.

"A driver has left the road, mounted the pavement and collided with a pedestrian," Superintendent Stuart Smith said.

The toddler was taken to Westmead Children's hospital with critical injuries but later died.

The elderly woman was not injured but was taken to Westmead Hospital suffering from shock.

Student nurse tried to revive toddler

Mariam Zreika, a student nurse who lived nearby, said she and her dad heard a crash and ran towards the woman and her grandson.

"I checked his pulse rate — there was no pulse at all, he wasn't breathing, nothing," she said.

"I pulled him on his side ... and when I did that he did take a few breaths in and out.

Police said the P-plate driver mounted the kerb before hitting the pedestrians. ( ABC News )

"As I was doing that, the police arrived and they put him back on his back and started resuscitation immediately."

Ms Zreika said the toddler had critical head injuries and cuts on his legs.

She said there were suggestions the little boy may have run out onto the road.

"The story was said that him and his grandma were crossing and he let go of her hand," she said.

"The car was coming and she [the driver] was trying to dodge him but he still got hit and she went into the brick wall."

Flemington Local Area Command Inspector Emma Watson said police were still trying to confirm the circumstances of the crash and were investigating whether the car mounted the curb or whether the boy ran out onto the road.

Police said a crime scene had been set up and the Crash Investigation team was investigating the incident but it was to early to determine whether the driver would face charges.