Emergency responders rushed to Milperra Road in Revesby around 3:20 p.m. following reports of an accident between Edgar Street and Mons Road.
Upon arrival, paramedics attended to a 12-year-old boy who had been struck by a vehicle in the westbound lanes.
The boy was subsequently transported to the hospital, where he remains in a serious yet stable condition.
According to police, the child was hit by the rear passenger side of a ute, which then left the scene.
Authorities suspect that the driver might not have realized the collision occurred.
In an effort to locate the vehicle, investigators have shared images of a ute, described as an orange or gold Nissan Navara. The vehicle is noted for its hard-top canopy, silver bullbar, and black wheel hubs.
The driver of the car is urged to come forward.