The initial statement said police tasked with protecting the complex at the heart of US government in Washington had ordered it be evacuated as they were “tracking an aircraft that poses a probable threat”.

It did not give further details.

The news became a top headline within minutes in the US, where the memories of Sept 11, 2001 attacks — which saw Al-Qaeda fly passenger jets into the World Trade Center in New York and the Pentagon in Washington — are still poignant.

But police swiftly issued a second statement to say the order had been given “out of an abundance of caution” and that there was “no threat” to the complex.

“The aircraft no longer poses a threat to the Capitol Complex and the USCP is now preparing buildings for reentry,” said the update from the US Capitol police.

Neither the House of Representatives nor the Senate, the chambers of Congress that are located in the Capitol, were in session at the time of the scare.

There was no immediate explanation for the order, but unverified reports suggested it could have come after a parachute display at a nearby sports stadium for “Military Appreciation Night”.

NBC’s Capitol Hill correspondent Garrett Haake tweeted that he had “Just watched some people parachute down over/near the US Capitol amid an evacuation order.”

NBC, citing police, said they were part of a demonstration by the Army Golden Knights at the nearby Washington Nationals Park stadium.

“Seems they might not have told Capitol Police they’d be in the airspace. One officer here told me she saw the small plane appearing to circle before the parachuters jumped,” Haake tweeted.

The stadium is roughly 2.5km from the Capitol.