A pedestrian who fell down while crossing the street was seriously injured Tuesday, when a driver ran him over as he lay on the ground.

The collision happened at 4:20 p.m. Tuesday, at the intersection of Hyde Street and Golden Gate Avenue. According to the San Francisco Police Department, a 78-year-old male pedestrian was walking in the crosswalk at Golden Gate, headed west, when he "collapsed in the crosswalk due to a possible medical emergency."

When the light turned green, police say that a 42-year-old driver headed south on Hyde continued through the intersection, striking the fallen man.

The pedestrian was transported to San Francisco General Hospital for treatment of injuries to the head and face that police characterize as life-threatening.

Police say that the driver remained at the scene of the collision, and was not arrested. As of publication time, police did not have any information on if the driver would be charged or cited in the case.