Navy officials announced at 1:30 p.m. that the shelter-in-place order was lifted after a thorough search of three buildings on the medical campus did not find anyone with a gun.
The armed man was reported on the fourth floor of Building 1 by an anonymous phone call at about 7:30 a.m., Navy spokesman Brian O'Rourke said. The caller hung up immediately after making the report, he said.
Naval security throroughly searched Building ,1 but as of 10 a.m., they had found no evidence of a gunman, according to O'Rourke. Because Building 1 is physically connected to Buildings 2 and 3 by pedestrian walkways and bridges, those two buildings were also being searched, O'Rourke said.
Just after noon, Navy officials confirmed that unused bullets were found on the hospital grounds.
"Four unspent bullets were discovered during security sweeps of the Naval Medical Center. Investigation is ongoing to determine any connection to the anonymous telephone call received earlier in the day."
Authorities said that they did not receive any reports of gunshots, but they ordered personnel to take shelter as a precaution. Staff and patients who were headed to the facility near Balboa Park were told to stay away until security officers finish searching the center.
A similar shelter-in-place order was issued on Jan. 26 after a staff member reported hearing gunshots in a building at the medical center. After an extensive investigation, authorities determined that the report was unfounded.