A security alert was issued at the U.S. Naval Medical Center in San Diego Thursday after a gunman was reported to have been seen inside the main hospital, but no shots were fired, a base spokesman said.

The base reported on its Facebook page that an “active shooter” was present on the base and advised all personnel and their families to avoid the area.

Base spokesman Michael Wiener told Reuters that military security were on the scene searching for a suspect.

A caller to the hospital reported seeing an unidentified man with a firearm on the fourth floor of the facility’s west wing, a nursing ward, prompting shelter-in-place orders to be issued for the hospital, Wiener said.

The medical center, about 2 miles (3 km) north of downtown San Diego, includes a 272-bed hospital and staff of more than 6,500 military and civilian professionals. San Diego is home to the U.S. Navy’s Pacific Fleet.

An active-shooter situation reported at the facility in January proved to be a false alarm.

(Reporting by Steve Gorman)