One person has died after slamming a vehicle into the security barrier surrounding the Capitol building.
The suspect is reported to have emerged from the vehicle brandishing a knife before being shot by a police officer.
The Capitol was locked down and a National Guard team was deployed as police instructed staff to remain indoors.
Two officers were struck by the vehicle and have been taken to hospital.
The entry point on Constitution Avenue where the vehicle struck the barricade is directly where Senators and their staff come to the Capitol each day, according to observers.
However Congress is currently in recess, meaning the majority of politicians are not at the Capitol complex today.
President Joe Biden left Washington earlier in the day for Camp David, the presidential retreat in Maryland.