A means veered off the road and into the barrier near the Library of Congress at Capitol Hill.
One director has received «multiple injuries» and has been taken to hospital.
The driver suffered boy injuries in the incident at about 1.30pm local time – 6.30pm UK occasion.
Witness reports state the vehicle slammed into fence and also impressed a police car.
US Capitol Police said: “The US Capitol Police are continuing to look into a suspicious vehicle located at Second Street and Independence Avenue SE.
“As a denouement of this investigation, the following road closures are in effect:
– Independence Avenue between Washington Avenue SW and Third Alley SE
– Pennsylvania Avenue between Second and Third Streets SE
– Second Passage between East Capitol and C Streets SE
– First Street between East Capitol Alley and Independence Avenue SE
“All staff and other personnel are directed to avoid this square footage until further notice.”
Officers on scene have reportedly effected out a «controlled explosion».
Katherine Gypson, reporter for VOA, said: «Police persist in to investigate suspicious vehicle at Independence & 1st, just heard planned buttoned detonation here on Capitol Hill.»