Police are investigating reports of a shooting at the NSA headquarters in Fort Meade, Maryland.
Local media footage shows damaged vehicles near a security gate on the NSA premises, and a tweet from the Anne Arundel County police referenced reports of a shooting.
Images show two damaged SUVs, one of which appears to be a police vehicle.
News 4 Washington has broadcast footage of a man being stretchered away from the scene, and other pictures appear to show a body under a white cover beside a vehicle.
The NSA has not yet released any details of the incident.
Around 40,000 people work at the facility, which is responsibility for covert communications intercepts.