Updated 5:05 PM EST
Officials at Naval Medical Center San Diego have lifted a shelter-in-place-order after a sweep of the center's administrative building turned up four unspent bullets, but no gunman.
The hospital complex had been under lockdown since Thursday morning, when an anonymous caller reported spotting an armed man on the medical center's campus. Officials pushed out an update on the center’s Facebook page advising hospital staff to shelter in place and telling employees and patients en route to return home.
Law enforcement officers with Naval Criminal Investigative Service and the San Diego Police Department spent the hours in lockdown conducting a sweep of the medical center's Building One, the main administrative center for the complex, said Lt. j. g. Madison McSweeney, a spokeswoman for Navy Region Southwest.
She could not specify what kind of rounds were discovered within the building, and said officials were still investigating how they got into the hospital.
Meanwhile, all operations have been restored at the center and the lockdown is over, McSweeney said.
While officials did not find an armed man and have not questioned or detained anyone at this point, McSweeney said it would be inappropriate to call the situation a false alarm, as officials continued to investigate.
It's the second time in three months that reports of a gunman have interrupted operations at the medical center, which employs about 500 staff. In January, staff members were instructed via Facebook to "run, hide or fight" after reports circulated of an active shooter. Those reports proved groundless.
Updated 12:56 PM EST
An official with Navy Region Southwest said that San Diego Police Department officials are in the process of searching Building One, which contains the main hospital complex for Naval Medical Center San Diego.
The official did not confirm media reports that a bullet had been found in the floor inside the building, but said law enforcement officers were still trying to verify reports of an armed man in the vicinity.
The entire base is secured and on lockdown, the official said, after an anonymous caller this morning reported a man with a firearm on campus. Staff and patients are being advised to stay award from the hospital as the investigation continues.
The official declined to comment on whether an active shooter situation was suspected, saying reports were still under investigation.
Staff members at Naval Medical Center San Diego were ordered to shelter in place after the hospital received a report of an armed man in the area.
In a post on its Facebook page Thursday morning, the center called the situation a "code white" and said staff and patients en route to the hospital were being advised not to come in until the scene had been cleared.
No shots had been fired, officials said, and security personnel were investigating the situation.
The alert comes two months after an active shooter was reported at the medical center Jan. 26. Officials engaged emergency protocols and posted a message to the center's Facebook page instructing staff to "run, hide or fight." Ultimately, however, that report proved to be a false alarm.