WASHINGTON, Feb 2 (AFP) - A suspected Chinese spy balloon has been flying over the United States for a couple of days, and senior US officials have advised President Joe Biden against shooting it down for fear the debris could pose a safety threat.

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."

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.

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.

China and the United States, the world's two largest economies, have experienced tensions of late, clashing over Taiwan, China's human rights record and its military activity in the South China Sea.

US Secretary of State Antony Blinken is due to visit China in the coming days.

A senior US defence official, briefing reporters on condition of anonymity, said the United States has had "custody" of the balloon since it entered US airspace a couple of days ago and has observed it with piloted US military aircraft.

US Defense Secretary Lloyd Austin, while traveling to the Philippines, convened a meeting of senior Pentagon officials on Wednesday to discuss the balloon incident.