A two-year-old girl has died in hospital after she was hit by a reversing car in Sydney's south-west.

The driver was "absolutely hysterical" after hitting the girl with a Kia car at the rear of a mechanic workshop in Campsie, police said.

Emergency services were called to Canterbury Road, just past Beamish Street, about 10.40am to reports of a toddler being hit by a car, a NSW Ambulance spokesman said.

The girl went into cardiac arrest and was rushed to Sydney Children's Hospital in Randwick in a critical condition, but later died.