US fighter jets on Saturday shot down an unidentified, unmanned high-altitude airborne object over northern Canada that had entered its airspace from Alaska, President Joe Biden said.

The decision in this regard was taken following a phone call between US President Joe Biden and Canadian Prime Minister Justin Trudeau, the White House said.

A day earlier, the US had shot down an object flying at the height of about 40,000 feet off the northern coast of Alaska on orders of Biden.

According to Pentagon Press Secretary Brig Gen Pat Ryder, North American Aerospace Defense Command (NORAD) detected the object over Alaska late Friday evening.

The White House said the object was closely tracked and monitored by NORAD over the last 24 hours and the President has been continually briefed by his national security team since it was first spotted.

"Out of an abundance of caution and at the recommendation of their militaries, President Biden and Prime Minister Trudeau authorized it to be taken down," the White House said, adding that Biden authorised US fighter aircraft assigned to NORAD to conduct the operation and a US F-22 shot down the object in Canadian territory in close coordination with Canadian authorities.

"The leaders discussed the importance of recovering the object in order to determine more details on its purpose or origin. President Biden and Prime Minister Trudeau commended NORAD’s and US Northern Command's strong and effective partnership and agreed to continue their close coordination to detect, track, and defend our airspace," the White House said.

Following the Biden-Trudeau phone call, two F-22 aircraft from Joint Base Elmendorf-Richardson, Alaska monitored the object over US airspace with the assistance of Alaska Air National Guard refuelling aircraft, tracking it closely and taking time to characterize the nature of the object, Ryder said.

Monitoring continued Saturday as the object crossed into Canadian airspace, with Canadian CF-18 and CP-140 aircraft joining the formation to further assess the object.

"A US F-22 shot down the object in Canadian territory using an AIM 9X missile following close coordination between US and Canadian authorities, to include a call today between Secretary of Defense Lloyd J Austin III and Minister of Defence Anita Anand,” Ryder said.

"As Canadian authorities conduct recovery operations to help our countries learn more about the object, the Federal Bureau of Investigation will be working closely with the Royal Canadian Mounted Police," he said.