A false alarm triggered a security lockdown for about two hours at Travis Air Force Base in northern California on Wednesday in response to erroneous reports of gunfire, base officials said.
A notice was first posted to official social media accounts of the base at about 3:30 p.m. local time (2330 GMT), reporting that the installation was "responding to a real world security incident," though no details about the nature of the threat were initially provided.
Television news footage broadcast live on local media from Travis showed a traffic backup near an entrance to the installation as authorities sealed off the base while personnel and their families were advised via Facebook and Twitter to "shelter in place."
Within two hours, however, an all-clear was issued by the base, located near Fairfield, California, about 50 miles (80 km) northeast of San Francisco.
"Travis Air Force Base emergency personnel responded to reports of gunshots at the Base Exchange. However, it was determined to be a false alarm. The base is no longer under lockdown," base officials said on Facebook.
The post added: "We take every security incident seriously."
Base officials could not immediately be reached by telephone for comment.
(Reporting by Steve Gorman in Los Angeles; Additional reporting by Bernie Woodall in Fort Lauderdale, Florida; Editing by Leslie Adler and Lisa Shumaker)