Three people have been arrested after a car was driven into the headquarters of the National Security Agency (NSA), America's secretive intelligence organisation.

In a black sport utility vehicle, the unnamed motorists reached the gate of the agency's campus in Fort Meade, outside Washington, on Wednesday at about 7am local time.

Gunfire rang out after the car approached the facility and the driver, a civilian and an NSA police officer were taken to hospital.

There is no indication yet that the incident was a terrorist attack, FBI officials said.

"There is no indication to think that this is anything more than an isolated incident," said Gordon Johnson, the Federal Bureau of Investigation's special agent in charge for Baltimore, close to where the incident took place.

"We have no reason to believe that there is any nexus to terrorism."