San Francisco General Hospital was placed on lockdown Thursday after an M80-type explosive was set off inside the facility, police said.
The incident prompted a heavy response from police and sheriff's deputies to investigate the incident, which was initially reported as a possible shooting inside the hospital. San Francisco Police Officer Grace Gatpandan later confirmed remnants of an M80-type explosive was found on the fifth floor of the hospital.
No injuries were reported during the incident, Gatpandan said.
Police are reviewing surveillance video and said no suspects have been detained.
During the response, deputies and police searched several floors and asked people to stay in their rooms.
No other information was immediately available.