Gunman reported at Naval Medical Center in San Diego

The centre went into a precautionary lockdown

People evacuate the Naval Medical Center San Diego on January 26, 2016. (Bill Wechter/AFP/Getty )

The Naval Medical Center in San Diego has been placed on precautionary lockdown after reports of a potential active shooter.

Officials issued a "code white" on Thursday after a caller reported seeing an armed man inside the facility.

“No shots have been fired. Security is investigating," officials said on Facebook. "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."

The anonymous caller matched the description of a patient seen with a weapon, one security official told USA Today.

Brian O'Rourke, a Navy spokesperson, told NBC 7 that the lockdown was issued as a precaution after the centre received an anonymous phone call reporting an armed man near the building at 7:35am PDT.

In January, an active shooter was also reported at the hospital, however, security officials determined it was a false alarm.