Chinese spy balloon flying over the United States, Pentagon says

A suspected Chinese spy balloon has been flying over the US for a couple of days, officials said on Thursday, in what would be a brazen act just days ahead of a planned trip to Beijing by US Secretary of State Antony Blinken.

Fighter jets were mobilised but military leaders advised President Joe Biden against shooting the balloon out of the sky for fear debris could pose a safety threat, advice Biden accepted, US officials said.

The United States took "custody" of the balloon when it entered US airspace and had observed it with piloted US military aircraft, one of the officials told reporters on condition of anonymity.

The incident recalls the lengths to which Beijing and Washington have been willing to go to spy on each other amid rising tensions between the superpowers.

"The United States government has detected and is tracking a high-altitude surveillance balloon that is over the continental United States right now," Pentagon spokesperson Brigadier General Patrick Ryder told reporters.

"The balloon is currently traveling at an altitude well above commercial air traffic and does not present a military or physical threat to people on the ground."

Blinken is expected to travel to China next week for a visit agreed to in November by Biden and Chinese President Xi Jinping. It was not clear how the discovery of the spy balloon might affect those plans.

The Chinese foreign ministry did not immediately respond to a Reuters request for comment.

US officials brought up the issue with their Chinese counterparts through diplomatic channels in Beijing and in Washington. "We have communicated to them the seriousness with which we take this issue," a US official said.

The current flight path would carry the balloon over a number of sensitive sites, but the official didn't give more details.

Another US official said the spy balloon had been tracked near the Aleutian Islands and Canada before entering the United States.

They've declined to say how high the balloon was flying but acknowledged it was operating above civilian air traffic and below "outer space".

US Senator Marco Rubio, the top Republican on the Senate intelligence committee, said the spy balloon was alarming but not surprising.

"The level of espionage aimed at our country by Beijing has grown dramatically more intense & brazen over the last 5 years," Rubio said on Twitter.

His fellow Republican, Senator Tom Cotton, called for Blinken to cancel his trip.

Republican House Speaker Kevin McCarthy said he would request a "Gang of Eight" briefing, referring to a classified national security briefing for congressional leaders and Republican and Democratic leaders of the intelligence committees. The Biden administration briefed Gang of Eight staff earlier on Thursday and has offered additional briefings, a US official said.

The news broke as CIA Director William Burns was speaking at an event at Washington’s Georgetown University, at which he called China the "biggest geopolitical challenge" currently facing the United States. 

Relations between China and the United States have soured in recent years, particularly following then-U.S. House Speaker Nancy Pelosi's visit to Taiwan in August, which prompted dramatic Chinese military drills near the self-ruled island.

Since then, Washington and Beijing have sought to communicate more frequently and prevent ties from worsening.