This story was updated at 1:30 p.m. ET.
The U.S. Navy said on Tuesday that it found no sign of a gunman or a shooting at its Naval Medical Center in San Diego, California, hours after it said it "received reports of an active shooter" in a building there.
"We did an initial clearing of the building and found nothing that would indicate any kind of dangerous situation," Captain Curt Jones, Commanding Officer of Naval Base San Diego, said at a press conference. "We are going back through and extracting people out of the building and ensuring that there is no threat," he added.
The reports first surfaced in a post on the Naval Medical Center of San Diego's Facebook page, which advised occupants at Building 26 to "run, hide or fight," and told all non-emergency personnel to stay away from the facility. The instructions mirrored lessons given at an active-shooter drill the facility held in December.
People were later seen emerging from the area with their hands above their heads.
#Breaking people coming out of Medical Center with hands up. #SanDiego pic.twitter.com/yXLRgEOtXC— Phillip Molnar (@PhillipMolnar) January 26, 2016
Police blocked traffic from entering the area while SWAT teams convened on the building. The reports, it later became clear, were based on the account of one witness according to a statement from the Navy.
A Naval Medical Center spokesman told local news outlet CW6 San Diego that the witness reported hearing three shots in the building's basement, prompting officials to treat the situation as one with an active shooter.
#BREAKING: Report of 3 shots fired outside of Building 26 at Naval Medical Center in Balboa Park. Public advised to stay away from area.— 10News (@10News) January 26, 2016
The Naval Base in San Diego also confirmed that it received information about the active shooter at the medical center building, and urged those in the area to shelter in place.
"If in immediate danger, hide or seek shelter in secure space. Barricade the door and dial 9 1 1. Silence phones and other devices. Stay away from doors and windows. Remain calm and quiet," read the alert.
The area where the gunshots were reportedly heard contains offices, barracks, a retail center and health-care operations, and hosts a combination of of active duty and civilian workers.
Reports of an active shooter @ Naval Medical San Diego. We are live @CW6SanDiego pic.twitter.com/hjMPaF8fKz— Amanda Shotsky (@AmandaShotsky) January 26, 2016
Local schools were briefly placed on lockdown following the reports, including San Diego High School, Garfield High School and Roosevelt Middle School. Less than an hour later, they returned to normal operation.