Earlier, there were reports that possible shots were fired in the area of 22nd Street and Potrero Avenue, but San Francisco police spokeswoman Officer Grace Gatpandan has since confirmed that no shots were fired. She also added that a remnants of an M80 type explosive and other illegal fireworks were found near the hospital.
There are no reports of injuries.
ABC7 News reporter Melanie Woodrow says people there tell her they heard a "boom," while others said the possible explosion sounded like a car accident.
Police and the FBI were on scene.
University of California at San Francisco police wrote on Twitter at 3:08 p.m. that evidence of illegal fireworks were found at the hospital and that people were still sheltering in place.
Stay with ABC7 News for the latest details on this developing story.
People here say same building was evacuated last night for a bomb scare (unconfirmed) pic.twitter.com/70uohR4Vq6— Melanie Woodrow (@MelanieWoodrow) July 7, 2016
Active scene here. Some say explosion sounded like a car accident. pic.twitter.com/AUQFwYhqzH— Melanie Woodrow (@MelanieWoodrow) July 7, 2016