No signs of gunfire were found after sweeps of a building at Naval Medical Center San Diego where a single witness reported hearing gunshots Tuesday morning.

"There was someone who thought they heard something and made reports," Capt. Curt Jones, commanding officer of Naval Base San Diego, said in a news conference. "We are investigating now as to what might have caused [the noise]."

The report was made from Building 26, which was cleared in a sweep after which personnel were evacuated .

"I would say that this is a case where we are pursuing the information we have to its logical conclusion and ensuring that everyone is safe," Jones said.

No patients were evacuated, said NMCSD commanding officer Capt. Jose Acosta. The hospital is not seeing patients for elective care today, he added, and patients in need of emergency or urgent care should visit another facility.

Naval Medical Center San Diego imposed a lockdown Tuesday morning after three gunshots were reported near a barracks and gym . Medical patients and staff sheltered in place while law enforcement descended on the sprawling medical facility in San Diego's Balboa Park.

Authorities "have not located any casualties or evidence of a shooting having taken place," Navy Region Southwest spokesman Scott Sutherland told Navy Times around 9:30 a.m. PST. "They are conducting a secondary, more thorough floor-by-floor sweep now."

Personnel remain sheltered in place, he said.

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A single witness reported hearing three shots at approximately 8 a.m. PST, according to a Tuesday afternoon Navy release, from the combination gym/barracks in the basement of Building 26.



"First responders and Navy working dog units are on scene clearing Building 26," the release said.

An 8:07 a.m. PST post from the medical center's official Facebook page read:

The "run, hide or fight" guidance is part of official Navy active shooter training, Jones said. NMCSD personnel last had a refresher in December.

"**!ATTENTION!** An active shooter has just been been reported in building #26 at Naval Medical Center San Diego. All occupants are advised to run, hide or fight. All non-emergency response personnel are asked to stay away from the compound, located at 34800 Bob Wilson Drive, San Diego, CA 92134."

The sentries reported shots fired at Building 26 and local police are responding. Agents from the Naval Criminal Investigative Service are en route but there was no confirmation of shots as of 9 a.m. local time. Building 26 also houses both the security, pass and ID office as well as the fitness center, according to the medical center's website. as yet, no confirmation of the shooting.

Base access was shut off to the public as SWAT teams, police cars, fire trucks and ambulances rushed onto NMCSD, according to local media accounts.

Personnel are sheltered in place, Navy Region Southwest spokesman Scott Sutherland told Navy Times. More information will be released as it becomes available.

Naval Medical Center San Diego, also known as Balboa Hospital, is located about seven miles north of Naval Base San Diego in the city's Balboa Park.

The 285-bed general medical and surgical hospital is home to a Navy Medical Support Training Center for hospital corpsman, is a training facility for the Uniformed Services University of Health Sciences, and is affiliated with the University of California, Children's Hospital San Diego, and Scripps Clinic and Research Foundation in La Jolla.

More than 6,500 active-duty, civilian, contractor and volunteer personnel work at the hospital, according to its website, serving thousands of patients a day and millions a year.

In the wake of the 2013 Navy Yard tragedy that left 12 dead, reports of shootings on Navy bases and facilities have continued as much as a half dozen times a year.

In early July, authorities responded to a report of a gunman at Navy Yard, which triggered a massive response in the heart of the nation's capital. The report was later ruled a false alarm.

Two weeks later, a lone gunman targeted military facilities in Chattanooga, Tennessee, killing five Marines and a sailor at a Navy Reserve center.

This is a developing story. Stay tuned for updates.