Relations between Washington and Beijing have nosedived following the shooting down of what the US alleges was a Chinese spy balloon -- China insisted it was an errant weather observation aircraft with no military purpose.

A number of unidentified aerial objects have subsequently been shot down over North America, though the US has not attributed them to China.

On Tuesday, Beijing doubled down on unsubstantiated allegations that the US has sent over 10 balloons since last year.

"The US has launched several high-altitude balloons from the US that made continuous round-the-world flights, illegally flying over the airspace of China and other countries on at least 10 occasions," foreign ministry spokesperson Wang Wenbin told a regular briefing.

"The US side should conduct a thorough investigation and give an explanation to China," he added.

Wang did not provide evidence of the alleged incursions, which he said started in May 2022.

He previously told journalists the incursions began in January that year.

Washington has denied Beijing's claims that it sent observation devices into Chinese airspace.

The US government alleges the balloon it shot down on February 4 was part of an ongoing, global "fleet" of Chinese espionage balloons.

It says the balloon was obviously a spy craft and that the debris is currently being plucked from the Atlantic Ocean for analysis.

Crews have recovered important sensor and electronics parts from the balloon, as well as large parts of the structure, the US military said Monday.

White House National Security Council spokesman John Kirby told reporters Monday the US is "not flying surveillance balloons over China".

"I'm not aware of any other craft that we're flying over into Chinese airspace," he said.