An active shooting forced the lockdown on Wednesday of Fort Stewart-Hunter Army Airfield, an army base in Georgia, the military base said in an alert posted on its social media pages.

The alert said there were casualties, but did not elaborate on the extent or number of those injuries. “Casualties have been reported,” it said, without providing further details.

The base, which is the home of the 3rd Infantry Division, said the active shooting took place in the 2nd Armored Brigade Combat Team area. The base was locked down just after 11 a.m., and law enforcement was on the scene.

It was not immediately clear whether there was more than one shooter, or whether anybody was in custody. Gov. Brian Kemp expressed concern for victims and their families and called the shooting a tragedy in a social media post.

The F.B.I. in Atlanta said on social media that its Savannah office was coordinating with the Army Criminal Investigation Division to offer assistance.

This is a developing story.