(CNN) The Naval Medical Center San Diego has asked people there to shelter in place after someone reported seeing an armed man, the southern California complex said on its Facebook page Thursday morning.

No shots have been fired, and security personnel are investigating, the center said.

"A caller to the hospital reported seeing an armed man on 4-West," the post reads. "... As a measure of precaution, staff are sheltering in place -- staff and patients en route to NMCSD are advised not to come to the hospital until the scene is cleared."

In January, a separate report of a shooting at the center turned out to be a false alarm , the military said.

Naval Medical Center San Diego bills itself as the largest military health care system in the western United States. Situated on 78 acres surrounded by San Diego's Balboa Park, the center has a 272-bed hospital, eight clinics for active-duty personnel and nine primary care sites for their family members.

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