The US has closed three airports and shut airspace off the South Carolina coast after the president said he would "take care of" a suspected Chinese spy balloon heading along that route.
Aviation authorities said they had stopped flights at the airports due to a "national security effort".
The military reportedly plans to bring it down over the Atlantic Ocean.
Joe Biden has faced intense pressure to shoot the balloon down since it first appeared across the US last week.
According to the US Federal Aviation Administration, one of the affected airports is Myrtle Beach International in South Carolina - the state the balloon was said to be heading towards.
Tracking website Flightradar24 showed US Air Force and Coastguard aircraft operating in the skies between Wilmington, North Carolina, and Myrtle Beach.
The coast guard has advised mariners to leave the area due to military operations "that present a significant hazard," the Associated Press reports.
The news agency, quoting unnamed officials, said President Biden had given the go ahead to bring the balloon down over the Atlantic Ocean, where debris can be retrieved.
The balloon's arrival over the US comes amid fraying tensions between Washington and Beijing, with Secretary of State Antony Blinken calling off a trip to Beijing over the matter.
Mr Blinken said the "surveillance" balloon's presence was "an irresponsible act". However, China - which says it is a weather ship blown astray - has urged "cool-headed" handling of the dispute.
The giant white balloon is thought to be over the Carolinas, close to the Atlantic coast.
In another development, the US reported a second Chinese balloon floating over Latin America on Friday.
China, which has expressed regret over the incident, said on Saturday it had "never violated the territory and airspace of any sovereign country".
In a statement, its foreign ministry played down the cancellation of Mr Blinken's visit and said neither side had formally announced such a plan.
It added that Beijing "would not accept any groundless conjecture or hype" and accused "some politicians and media in the United States" of using the incident "as a pretext to attack and smear China."
According to US officials, the balloon floated over Alaska and Canada before appearing over the US state of Montana, which is home to a number of sensitive nuclear missile sites.
The incident angered top US officials, with Mr Blinken saying he had told Beijing the balloon's presence was "a clear violation of US sovereignty and international law" and "an irresponsible act" on the eve of his visit to China.
America's top diplomat had been set to visit Beijing from 5 to 6 February to hold talks on a wide range of issues, including security, Taiwan and Covid-19. It would have been the first high-level US-China meeting there in years.