A boy is in an induced coma after his bicycle was hit by a car and dragged 20 metres along the road in Sydney's south west last night.

The 13-year-old was riding his bike along the footpath on Sackville Street at Canley Vale, while his father walked behind him, about 8.30pm.

Police said the boy was crossing Pevensey Street when a car turning right out of Sackville Street hit the boy as he rode onto the road.

The car dragged the bicycle about 20 metres along the road before driving off without stopping, police said.

The boy was taken to Westmead Children's Hospital with a fractured skull and was in an induced coma this morning.

Police are urging anyone who saw the collision to call Crime Stoppers on 1800 333 000. Callers can remain anonymous, police said.