Authorities say reports of a possible gunman led to a lockdown at a U.S. Army Reserve training facility in Northern California as police search a residential area at the site.

Alameda County sheriff's Sgt. Ray Kelly said there were initial reports of possible shooter at the Camp Parks Reserve Forces Training Area, but no one has been spotted and those reports haven't been confirmed.

No gunshots have been heard. Multiple police agencies from areas east of San Francisco are searching the area.

Camp Parks Reserve Forces Training Area is a semi-active mobilization and training center for U.S. Army Reserve personnel.