The accident was reported at 7:08 a.m. at the intersection of Seventh and Harrison streets.
The wheelchair-bound pedestrian was crossing Harrison Street north in the crosswalk with a green light but did not make it across the street before the light turned red, police spokesman Officer Albie Esparza said.
While cars in three of the lanes traveling west on Harrison Street stopped, a vehicle in the fourth lane struck the pedestrian, who was taken to San Francisco General Hospital to be treated for the life-threatening injuries, Esparza said.
The driver of the car that struck the pedestrian stopped at the scene and cooperated with police, Esparza said.
"Motorists are reminded when pedestrians are crossing the street lawfully and the light does turn colors, traffic shall yield to the pedestrian to allow them to safely continue crossing the street before they proceed," he said.