Montgomery County police say a gunman has entered the Discovery Communications building in Silver Spring and has taken at least one person hostage.
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Footage from WJLA-TV showed police SUVs and cruisers with their lights on.
Cpl. Dan Friz told the channel that a gunman was in the building.
A person inside the building told The Associated Press that the man had something strapped to his chest and has hostages. The person refused to be identified, saying people inside have been told not to speak to the media.
Police did not immediately return calls from The Associated Press.
Sheree Mixell, assistant special agent in charge of the Baltimore field division office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, said agents are responding to the scene.
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