All shelter in place orders at the Naval Medical Center San Diego following reports of an active shooter have been lifted with no evidence of an attacker or gunfire found, authorities said Tuesday.
The order was lifted for a last building on the campus about 4 p.m. following a search by police and K9 units, officials said.
No sign of casualties or other evidence of a shooting were been found in a sweep of the entire facility.
There is "nothing which substantiates" reports of a shooting, said Navy Capt. Curt Jones, commanding officer of Naval Base San Diego, at a news conference Tuesday.
Reports of a possible active shooter about 8:22 a.m. caused the medical center to issue an alert telling hospital occupants to "run, hide or fight."
"Apparently someone said they heard three shots in the basement of Building 26. Maybe they did or not is not the point; that's what they reported, so that's why we responded accordingly," said Jon Nylander, Navy spokesman. "We haven't gotten any reports of any injuries."
The Naval Base San Diego alerted personnel to reports of an active shooter via Facebook, and advised all non-emergency personnel to avoid the compound in the 34800 block of Bob Wilson Drive.
"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 hospital wrote.
"If you are in the vicinity, shelter in place. If in immediate danger, hide or seek shelter in secure space. Barricade the door and dial 911. Silence phones and other devices. Stay away from doors and windows. Remain calm and quiet."
Law enforcement also began searching the hospital with a K9 unit, according to Nylander, as part of a "top down" search of the building. The basement is a combination gym and barracks, he said.
U.S. marshals, the Chula Vista Police Department and the California Highway Patrol are assisting, authorities said.
The medical center posted an update shortly after 9 a.m. saying that all childcare facilities were secured:
The Navy Medical Center San Diego comprises more than 400 physicians, 760 registered nurses and thousands of civilian and military personnel. The 272-bed facility offers medical care to active duty members and their families from Miramar to El Centro.
Located at the southeast corner of Balboa Park, the hospital has a dental clinic for active duty service members, a virtual reality lab for post-traumatic stress syndrome treatment and recreational facilities.
The facility boasts the only U.S. Navy medicine amputee center in the Western Pacific.
The hospital can treat more than 250,000 San Diego residents.
Three San Diego Unified schools were temporarily placed on lockdown "as a precaution," the district announced on Twitter.
Roosevelt Middle School and San Diego and Garfield high schools were all temporarily locked down as a precaution, the district said.