A Bronx psych patient made a run for it from an ambulance and fled to a nearby parking garage, where he leaped from the second floor and was critically injured, police said Friday.

The 27-year-old man was being transported by private ambulance from Jacobi Medical Center to Montefiore Medical Center around 3:40 p.m. Thursday when he punched the ambulance driver in the face and ran off from the ambulance, police sources said.

The patient, who was being transported for a psychological evaluation, made his way to the second floor of a parking garage on Pelham Parkway South near the medical center and jumped, sources said.

The man fell approximately 20 feet onto a loading dock below, police said.

He suffered trauma to the head and was taken to Jacobi in critical condition.

Police are investigating the incident.