A 9-year-old boy on an electric scooter was seriously injured in East Harlem when he was struck by an FDNY ambulance rushing against traffic to a priority job, cops and sources said.

The ambulance had its lights and sirens on, and was turning right from East 99th Street onto First Avenue when it struck the boy, who was alone, cops said.

He was taken to the hospital by another ambulance, and treated for a mangled leg, a broken femur, pelvic injuries and internal bleeding, sources said. He was in critical but stable condition Saturday night.

The EMT driving the ambulance was distraught, sources said.

The accident came hours after another young child was struck by a vehicle on Bailey Avenue near West 230th Street in Kingsbridge in The Bronx, suffering only pain and bruising, cops said.

Authorities did not release the injured kids’ names.