A man racing a dirt bike illegally in Hunting Park mowed down a 5-year-old boy Sunday, leaving the tot with a broken collarbone and ribs, police said.

Instead of coming to the injured boy's aid, the dirt-biker's two dirt-biking pals stopped to help their friend back onto his toppled bike and then all three sped off, leaving the boy's mother screaming for help.

The hit-and-run happened at 5:05 p.m. in a grassy area at Ninth and Cayuga streets, near the park's entrance, police said. The boy was standing next to his mother's parked car, waiting to climb inside, when the three dirt-bikers roared toward him, police said. After he was hit, he was rushed to St. Christopher's Hospital for Children, where he remains in serious but stable condition.

The biker who hit the boy was a Latino man in his early 20s, wearing a white t-shirt, blue jeans and navy or black sneakers. He rode a red and white dirt bike. He and his two accomplices were last seen speeding west through the park toward Old York Road. Anyone with information about this incident should call the Accident Investigation Division at (215) 685-3180.

Hunting Park often is overrun by illegal riders on quads and dirt bikes whenever the weather warms.

City Council passed a law last fall setting stiff fines for anyone riding an ATV or dirt bike on public property, including parks. The law, which requires police to confiscate the offender's vehicle for disposal, took effect last month. But the Police Department couldn't provide figures on how many citations have been issued nor vehicles seized since enforcement started.