A United States F-22 fighter jet has shot down an unidentified object flying over Alaska less than a week after the military brought down a Chinese balloon that had flown across the US.

A sidewinder missile brought down the object, which was about the size of a small car, the Pentagon’s chief spokesman US Brigadier General Patrick Ryder said on Friday.

President Joe Biden ordered the action, which was announced from the White House – rare presidential-level involvement given initial accounts suggesting the object did not pose a military threat and was fairly rudimentary.

On February 4, another US F-22 fighter jet shot down what the US government called a Chinese surveillance balloon off the coast of South Carolina following its week-long journey across the US and parts of Canada.

Republicans and even some of Biden’s fellow Democrats criticised the president for waiting before he acted against that first balloon.

The incident set off a diplomatic crisis between the world’s two largest economies and caused US Secretary of State Antony Blinken to cancel a planned trip to Beijing.

Few details released

The Pentagon and the White House declined to give a detailed description of the latest object to be shot down, saying only that it was far smaller than the Chinese balloon.

The Pentagon said it was flying at about 12,190 metres, posing a risk to civilian air traffic.

“We don’t know who owns this object,” White House spokesman John Kirby said.

The object was shot down over Alaska’s far northeast near the Canadian border where it had been travelling in a north-easterly direction.

The Pentagon said it was first detected on Thursday using ground radars, prompting a close inspection by fighter jets.

Ryder said US pilots who flew alongside it determined no human was onboard, that it was incapable of manoeuvring and did not resemble an airplane.

‘It wasn’t an aircraft’

“It wasn’t an aircraft per se,” Ryder told a news briefing.

Ryder and other officials would not say whether it could simply be a weather balloon or another type of balloon.

Asked why Biden’s authorisation was necessary, Ryder acknowledged the US military commander overseeing North American airspace had the authority to shoot down objects that posed a military risk or risk to the people.

“In this particular case, it was determined that this posed a reasonable threat to air traffic,” Ryder said.

Since the 60m-high Chinese high-altitude surveillance balloon was shot down, US officials have been scouring the ocean to recover debris and the undercarriage of electronic gadgetry.

Ryder told reporters “a significant” amount of the balloon had already been recovered or located, suggesting US officials could soon have more information about any sophisticated Chinese espionage capabilities aboard the vessel.

“That will be very beneficial to us learning more about it,” Ryder said.

-AAP