UPDATE 1:56 p.m. ET: The Montgomery County Police Department said police operations at Walter Reed are complete and there is no evidence of any gun discharge.
UPDATE 1:10 p.m. ET: A police official told reporters that there is no indication of a shooting or any injuries at Walter Reed.
Authorities are still completing their search of the facility.
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Security officers are responding to an unconfirmed report of an active shooter at Walter Reed military hospital outside Washington, D.C.
The Montgomery County Police Department said a call came in at 10:48 a.m. about a single gunshot heard on the campus.
Personnel have been ordered to shelter in place, the U.S. Navy's Twitter feed said.
News cameras overhead showed some people being escorted out with their hands up.
Developing.