Canada said Thursday it was working with the United States to track a high-altitude surveillance balloon, and it was monitoring a "potential second incident."

"A high-altitude surveillance balloon was detected and its movements are being actively tracked," Canada's defence department said in a statement.

"Canadians are safe and Canada is taking steps to ensure the security of its airspace, including the monitoring of a potential second incident."

"Canada's intelligence agencies are working with American partners and continue to take all necessary measures to safeguard Canada's sensitive information from foreign intelligence threats."

The Pentagon said earlier Thursday it was tracking a Chinese spy balloon flying high over the United States.

A US official said the balloon had flown over the northwest United States, where there are sensitive airbases and strategic nuclear missiles in underground silos.

The Canadian statement did not reference China.

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