5:10 p.m. UPDATE: Travis Air Force Base is now clarifying its earlier statement, saying it was a report of an active shooter that started the lockdown. No shooter was found.

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4:50 p.m. UPDATE: A Travis Air Force spokesperson has confirmed the active shooter situation started at the base exchange. Officials declined to say if the situation was ongoing or whether there were any casualties.

Aerial video from the scene shows a calm and orderly effort to get people out of the shopping center by security officials.

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4:30 p.m. UPDATE: CBS13’s Steve Large is near the base and can hear the alerts for the lockdown being called out over the loudspeaker.

Loudspeaker outside Travis Air Force Base: Real World…LockDown. pic.twitter.com/WALDZNTFPs — stevelarge (@largesteven) June 14, 2017

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4 p.m. UPDATE: A witness at the scene says there is an active shooter situation at the shopping center on base.

Security crews are out in the parking lot, bringing people outside from the shopping center.

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FAIRFIELD (CBS13) — Travis Air Force Base is under a security alert due to a “real world security incident.”

The Air Force base had a training exercise planned for Wednesday and Thursday, but this is not related to it.

Security alert @Travis60AMW. Shelter in place. Lock doors/windows. Await further info. Follow Travis Facebook page for updates. — Travis AFB Official (@Travis60AMW) June 14, 2017

The public is being asked to stay away from the base while emergency responders do their job.

Fairfield Police say they are not responding to the incident and are deferring to the base.

Beale Air Force Base in Yuba County is not on lockdown.