Wright-Patterson Air Force base, just east of Dayton, Ohio, went into lockdown at approximately 9:25 pm (0125 GMT Friday), the 88th Air Base Wing, based at Wright-Patterson, said on Twitter.

At that time "emergency responders responded to a report of an active shooter in the National Air and Space Intelligence Center in Area A at WPAFB.

"Security Forces are currently sweeping the building. The base is on lockdown."

According to local WHIOTV, the base's giant loudspeakers blared out the message of "Lockdown Lockdown Lockdown" at intervals so loudly that it could be heard outside the base.

"We understand there are concerns and questions. Our first priority is to protect our people," officials tweeted.