Naval Medical Center San Diego imposed a lockdown Tuesday morning after a gunman was reported near a barracks and gym, according to the authorities there. 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. "They are conducting a secondary, more thorough floor-by-floor sweep now."

Personnel remain sheltered in place, he said.

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:

**!ATTENTION!** An active shooter has just been been reported in building #26 at Naval Medical Center San Diego. All...

Posted by Naval Medical Center San Diego (NMCSD) on Tuesday, January 26, 2016

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, according to the medical center's website.

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

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 Navy website, serving thousands of patients a day and millions a year.

In the wake of the 2013 Navy Yard tragedy, 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.

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