As a fire was reported several blocks away from the building under a nearby bridge, lawmakers and other Capitol Hill personnel were informed immediately as smoke could be seen from a distance.

They were told to stay inside and stay away from exterior windows and doors. 

Washington fire and emergency medical services said on Twitter that they responded to "an outside fire in the 100 block of H St SE that has been extinguished."

There were no injuries, it said, adding: "This accounts for smoke that many have seen."

Later, the fire department said the fire involved a homeless woman burning propane in her tent beneath the freeway, explaining reports of an explosion.

The woman sustained a non-life-threatening injury but refused hospital treatment, instead asking for help from the local Red Cross, the department said

The US Secret Service said on Twitter that there is no threat to the public, and advised people who live, work, or plan to visit the Washington area on inauguration day check the latest road closure map.

Personnel involved in incoming President Joe Biden's inauguration rehearsal also evacuated the area.

Capitol Hill is currently operating as a military zone ahead of Biden’s Wednesday inauguration, with increased security after supporters of outgoing President Donald Trump clashed with the police and stormed the building on Jan. 6.

The violent riot resulted in the deaths of five people.

There are seven-foot barriers staged around the Capitol and nearby office buildings, including the Supreme Court.