Authorities lifted a lockdown Tuesday at one of the U.S.'s largest naval medical facilities after finding no gunman or signs of a shooting initially reported by a Department of Defence employee.

The report grabbed attention across the nation and led to the shutdown of the Naval Medical Center San Diego in Balboa Park, near the San Diego Zoo, and three nearby schools.

Fears were heightened when the medical centre posted on its Facebook page that, "An active shooter has just been reported in building #26 at Naval Medical Center San Diego. All occupants are advised to run, hide or fight."

The unidentified Department of Defence employee who made the report said the gunshots were heard just before 8 a.m. PT on the sprawling 30-hectare campus, where Building 26 houses administrative offices, a gymnasium and dormitories for combat-wounded veterans in long-term care. As many as 800 people work in the building.

All non-emergency personnel were asked to stay away from the area and traffic backed up around the facility during the morning rush hour.

Military personnel searched the structure for about two hours before saying there were no initial signs of a shooting.

The base remained on lockdown for hours as military police went room to room and led personnel out of the building.

"As of right now we have found absolutely nothing that indicates there were any shots fired," Capt. Curt Jones, commanding officer of Naval Base San Diego, said during the search.

Jones said the employee made the report in person about shots being fired. There was construction going on nearby, but Jones said he did not know if that noise was mistaken for the sound of gunshots.


The 272-bed hospital and ambulatory complex is located in the southeast corner of Balboa Park, about four kilometres from downtown San Diego. Centre staff includes more than 6,500 military, civilian, contractor and volunteer personnel.

The navy took appropriate steps in response to the report by locking down the facility and warning people of a possible shooter, he said. Numerous agencies — including the FBI, Homeland Security and police departments — offered assistance, he added.

"Obviously there's been numerous events throughout the country and truly around the world, so we take this all very, very seriously," he said.

The lockdown was lifted around 2 p.m. local time, but the building remained closed while the investigation continued.

After the initial search, TV images showed uniformed navy personnel walking outside the medical facility. Their hands were in the air and they were being patted down by base police as a precaution.

More than 6,500 military, civilian, contractor and volunteer personnel work at the 272-bed, multi-specialty hospital and ambulatory complex.


Navy personnel leave a building with their arms up as a SWAT team clears a building adjacent to Building 26 at the Naval Medical Center. (Mike Blake/Reuters)

Sharie Jarsulic, a teacher at the base child care centre, waited in her car outside the main gate after being denied entry. Her work day begins after employees drop off about 200 children.

The response was justified, she said, pointing out that the hospital treats mentally ill people and military members traumatized by war.

"They acted the right way," she said while waiting for the gate to reopen. "It could be someone inside or in the barrack and they could have just went off."

The facility is affiliated with 19 civilian nursing schools, training more than 400 students per year in clinical rotations. It is a leading centre for medical research and has treated numerous combat veterans and Afghan and Iraqi civilians from the recent conflicts.