A 30-Stockton Muni bus was struck by a cable car near Columbus Avenue and Chestnut Street at about 4 p.m., spokesman Paul Rose said.
The driver apparently lost control of the cable car after it couldn't keep its grip on a worn cable, Rose said.
Two passengers in the crash complained of minor injuries, but refused treatment.
Drivers in the bus and cable car will undergo drug and alcohol testing, Rose said, but no administrative leave has been planned.
Crews were still working to restore service on cable cars near the crash as of 6:30 p.m.
Shuttles were put in place to assist passengers impacted by the lack of service, Rose said.