The White House has been placed on lockdown after an "uncontactable" aircraft sparked panic in the US capital.
CNBC reported earlier that an airspace violation had been reported, causing a swift defensive reaction from US authorities.
NBC reported earlier that North American Aerospace Defense Command (NORAD) had tasked aircraft to respond to the security alert.
Reporters trying to enter the White House were there was an "emergency", tweeting that agents have locked everything down and begun blocking roads around the Capitol in Washington DC.
A CNN reporter said the lockdown had been lifted shortly after the reports of the aircraft entering restricted airspace prompted authorities to mount a major emergency response.
An official told CNN the aircraft "is not known to be hostile at this time".
Those already in the White House had been told to stay put, according to tweets from reporters at the scene.
The broadcaster has also reported that a security alert was raised at the Capitol building.
US reports say all Government buildings are being evacuated.
Reporters in the White House briefing room were tweeting that it had been locked.
Some reporters were evacuated to the White House's North Lawn.
