Shots have been fired outside the headquarters of the National Security Agency, according to US media.
Gunfire reportedly rang out after a black SUV pulled up at the entrance to the facility in Fort Meade, Maryland.
Local media report that three people were shot and a suspect was arrested in the incident outside America's electronic espionage agency.
But Fort Meade police spokesman Larry Whitley said one person had been injured and transported to hospital.
Anne Arundel County police tweeted at 07:30 local time (12:30 GMT) that it was responding to "a possible shooting" at the complex.
CBS News images showed the black sports utility vehicle, with what appeared to be bullet holes in the front windscreen.
US President Donald Trump has been briefed on the incident, according to a White House spokeswoman.
"Our thoughts and prayers are with everyone that has been affected," said a White House spokeswoman, Lindsay Walters.
In March 2015, one person was killed and another seriously wounded after driving a vehicle up to the NSA's gate, ignoring commands to stop.
News reports later suggested the two occupants of the vehicle may have been under the influence of drugs after attending a party.