There are reports of an active shooter at a US Navy hospital in California.

Witnesses reported hearing gunshots in the basement of Building 26 Naval Medical Center in San Diego, California, prompting emergency services to evacuate the building, where injured soldiers are treated.

The hospital issued a stark message on its official Facebook page, alerting people inside to reports of a shooter, and urging them to take action, be it "run, hide or fight."

**!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

There are no reports yet of injuries, and security forces did not find any evidence of a shooting after an initial sweep of the building. They are currently conducting a second "top to bottom" search of the building, according to the LA Times.

"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," US Navy spokesman Jon Nylander said. "We haven’t gotten any reports of any injuries."