Update (12:13 p.m.): Joint Base Andrews confirmed reports that there was no active shooter in a statement on Twitter:
The incident that occurred this morning has been cleared as of 10:40 a.m. First responders determined there was no threat to the base. JBA was scheduled to conduct a no-notice active shooter exercise in the late morning on the opposite side of the base. However, reports of a real-world active shooter situation at the medical facility were miscommunicated before the exercise was able to begin. There was a misidentification of the security forces emergency services team who were conducting a routine inspection of the facility.
The base commander, Colonel Brad Hoagland, commended the on-scene response to the situation:
"Fortunately, this was not a life-threatening situation, Hoagland said. We take all threats seriously and reacted to ensure the security of those on the base. I applaud the quick reaction of our first responders in keeping the safety of our JBA family a number one priority. In addition we thank our local authorities for quickly standing by and offering their assistance."
The base's intense reaction to the false report is understandable, considering the recent terrorist attacks in Orlando and Istanbul that resulted in dozens of fatalities.
Update (11:00 a.m.): Reports have surfaced saying that there actually was no active shooter. According to The Washington Post, "A federal law enforcement official said there was 'not a shooter,' and that the confusion is believed to have stemmed from a drill happening at the same time. The official said someone in a different building saw the drill and called 911, and because of that call, authorities treated it as a real incident."
Joint Base Andrews in Maryland, the home of Air Force One, was put on lockdown after reports surfaced of an active shooter on the base Thursday morning. The lockdown was lifted and the "all clear" given, with the exception of Malcolm Grow Medical Facility, about two hours later.
JBA's Twitter account declared the base on lockdown and told all personnel to take shelter:
Another tweet said the incident was taking place at the Malcolm Grow Medical Facility, and that first responders were on the scene:
According to further reports, the call for a lockdown occured around the time a training exercise was scheduled to take place, but according to the base's Facebook page, authorities were responding to a "real-world active shooter":