[CLYDE, United States] President Donald Trump on Thursday announced he had ordered a 10 per cent tariff on Canadian aluminum be reimposed, saying America's key trading partner was flooding the US market with the metal.

"Canada was taking advantage of us, as usual," Mr Trump said in a speech at a Whirlpool washing machine factory in Clyde, Ohio.

"I signed a proclamation that defends American industry by reimposing aluminum tariffs on Canada," he said.

Mr Trump had exempted Canadian products from the tariffs as part of the USMCA free trade deal with Mexico and the United States, on condition that they "not flood our country with exports and kill all of our aluminum jobs."

"Canadian aluminum producers have broken that commitment," he said.

The tariffs, which take effect on August 16, are in response to what Washington called a "surge" in aluminum imports from Canada over the past year which "threatens to harm domestic aluminum production."

GET BT IN YOUR INBOX DAILY

Start and end each day with the latest news stories and analyses delivered straight to your inbox.

Sign UpVIEW ALL

"I have determined that the measures agreed upon with Canada are not providing an effective alternative means to address the threatened impairment to our national security from imports of aluminum from Canada," Mr Trump said in his proclamation.

Ottawa has long rejected the national security concerns coming from a close ally - the two nations have been joined in a free trade area since 1994.

Canada's Prime Minister Justin Trudeau declined to travel to Washington to join in the USMCA launch ceremony early last month, after Mr Trump floated the idea of again hitting the country with the tariffs.

AFP