SAN FRANCISCO (CBS SF) — A report of possible shots fired that triggered an evacuation at San Francisco General Hospital Thursday afternoon was probably caused by someone setting off a firecracker, police said.

Reports came in of a possible explosion or sound of shots fired in a hospital building at 955 Potrero Avenue at around 2 p.m., according to police Capt. Dan Perea.

San Francisco Police Department public information Officer Grace Gatpandan tweeted about the report at 2:20 p.m.

The report drew a massive police response, with upwards of three dozen police units converging on the hospital.

Police worked with the sheriff’s department, University of California at San Francisco police and the fire department to evacuate and search the two buildings at that address.

Officers found nothing but the remnants of one expended M-80 firecracker in a fifth floor hallway, Perea said.

“The good news is that there was no shooting inside the hospital today,” he said.

No injuries were reported. Police did not have any suspect information but said they would be looking for surveillance video footage from the area.

Gatpandan later confirmed that debris from fireworks was found on the 5th floor inside SF General.

Hospital spokesman Brent Andrew said Buildings 80 and 90, where the incident occurred, house outpatient clinics. Hospital operations outside of those buildings were not affected by the evacuation.

Andrew said that no one appeared to have been in the hallway to see the firecracker go off, although at least one person down the hall heard it. The explosion set off a fire alarm.

Despite the incident, Andrew said security at the hospital was not a problem.

“We are very fortunate to have the sheriff’s department here providing security,” Andrew said. “Considering the openness of the campus and considering the number of people who come through here every day, we feel very secure.”