A boy has died after he was hit by a car at Westmead on Tuesday afternoon, police said.

The boy, 4, suffered fatal brain damage after he was hit by grey Mazda 6 as he tried to cross Hawkesbury Road with his mother about 4.30pm.

Paramedics performed performed CPR before taking him to The Children's Hospital, Westmead.

He was pronounced dead a short time later.

The child's mother suffered minor injuries and another boy, 6, who was with the woman was not injured.

A woman, 46, who was driving the Mazda was not injured but taken to hospital for mandatory blood and urine tests.

Holroyd police continue to investigate and have asked any witnesses tom contact Crime Stoppers.