U.S. President Donald Trump is moving to impose tariffs of 50 per cent on a wide range of Canadian exports, a dramatic ramping up of his trade war against his northern neighbour.

Axar.az reports, citing CBC, the 50 per cent rate is being imposed in response to what a senior administration official described as Canada's retaliation against U.S. trade policy and its discrimination against U.S. motor vehicles, dairy and alcohol.

"This is not a trade war with Canada, these are defensive measures," the official said in a conference call with reporters Monday afternoon.

The new rate, laid out in three presidential proclamations, is set to take effect in 30 days.

While energy, potash, critical minerals and fish would be exempt, other products that until now have been allowed into the U.S. tariff-free under terms of the Canada-United States-Mexico Agreement (CUSMA) would be hit.

The 50 per cent tariff is five times higher than the current duty imposed on the small portion of Canada's exports to the U.S. that don't comply with CUSMA's rules of origin regulations.