Canadian Prime Minister Justin Trudeau says that investigators are hunting for the wreckage of the flying object shot down by a US fighter jet over Yukon territory, as the US Senate's top lawmaker, suggests it and another flying object shot down off the coast of Alaska, both appeared to be balloons.

"Recovery teams are on the ground, looking to find and analyse the object," Mr Trudeau said.

He gave no hint as to what it was but said it "represented a reasonable threat to the security of civilian flight".

"The security of citizens is our top priority and that's why I made the decision to have that unidentified object shot down," he said.

US Senate Majority Leader Chuck Schumer provided a bit more detail to US broadcaster ABC, saying that American national security officials believe the object destroyed over Canada — as well as another flying object shot over the sea ice near Deadhorse, Alaska on Friday — were both balloons.

"They believe they were [balloons], yes, but much smaller than the first one," Mr Schumer said, referring to the balloon that was shot down off the coast of South Carolina last Saturday — a big, white, eye-catching inflatable whose trip across the US airspace at the beginning of the month sparked an international incident.

The White House said only that the recently downed objects "did not closely resemble" the Chinese balloon, echoing Mr Schumer's description of them as "much smaller."

US continues search for balloon debris

American officials have accused the Chinese of using the 60-metre-high balloon for surveillance. China's government has said it was a civilian research vessel that went off course and has condemned its destruction.

US officials have been scouring the ocean to recover debris and electronic gadgetry since the original balloon's destruction.

Mr Schumer said he was confident US investigators would get to the bottom of what it was being used for.