A suspected Chinese spy balloon has been flying over the United States for several days, U.S. officials said Thursday.
Pentagon spokesperson Brigadier General Patrick Ryder said the balloon is traveling "well above commercial air traffic and does not present a military or physical threat to people on the ground."
North American Aerospace Defense Command (NORAD) is tracking the balloon, but officials would not say where the aircraft is currently.
NORAD said in a statement that it "continues to track and monitor" the balloon "closely."
The detection of the balloon came just days before U.S. Secretary of State Antony Blinken's long-planned trip to China. It was not immediately clear how the discovery of the balloon might affect his travel plans.
The balloon was spotted Wednesday over the northwestern state of Montana, which houses one of the three U.S. Air Force bases that operate and maintain intercontinental ballistic missiles.
Air traffic out of the Billings, Montana, airport briefly came to a halt Wednesday as the U.S. mobilized fighter jets to track the balloon.
Military officials advised against shooting down the balloon because of the damage its debris could cause to people on the ground.
The spy balloon, Pentagon officials said, traveled to the U.S. from China across the Alaska's Aleutian Islands and through northwest Canada.
Canada said Thursday that it is working with the U.S. to track a high-altitude surveillance balloon, and it was monitoring a 'potential second incident.'
Canada's Defense Department said in a statement, "Canadians are safe, and Canada is taking steps to ensure the security of its airspace, including the monitoring of a potential second incident.'
The balloon above Montana was not the first Chinese balloon spotted in the U.S, but this one seems to be hovering over locations longer than before, according to a military official.
U.S. officials said measures have been taken that would prohibit the massive, unmanned reconnaissance balloon from gathering any intelligence, but officials have not said what those moves are.
Peter Layton, a fellow at the Griffith Asia Institute in Australia and former Royal Australian Air Force officer, told CNN, "An advantage of balloons is that they can be steered using onboard computers to take advantage of winds and they can go up and down to a limited degree. This means they can loiter to a limited extent."
In contrast, Layton said, "A satellite can't loiter and so many are needed to crisscross an area of interest to maintain surveillance." The balloon is likely gathering information on U.S. communication systems and radars, he said.
A senior U.S. official told reporters that the goal of the spy balloon was "surveillance and clearly they're trying to fly this balloon over sensitive sites ... to collect information.'
Both the U.S. and the Soviet Union used similar surveillance balloons during the Cold War, Craig Singleton, a China expert at the Foundation for Defense of Democracies, told Reuters about the aircraft's inexpensive intelligence gathering.
Spy balloons usually operate at 24,000-37,000 meters, far above the operating levels of commercial airline traffic and fighter jets.