The crash was reported at Baker and Hayes streets. The San Francisco Fire Department said on social media that the four people had minor to moderate injuries and asked the public to avoid the area while police investigated.
Photos from the scene showed police tape across the roadway, several police vehicles and two damaged vehicles: a black station wagon with damage to its passenger side and a black three-wheeled vehicle stopped near a crosswalk.
Police had not released additional details about what caused the crash, whether anyone was cited or arrested.
The crash happened near the Panhandle, a busy area with residential traffic, transit stops and bicycle and pedestrian activity.