Canada on Tuesday (Aug 25) announced retaliatory tariffs on C$27.6 billion (US$19.94 billion) worth of United States goods, matching dollar-for-dollar new duties imposed by Washington, and unveiled financial support for Canadian businesses and workers caught in the escalating trade war.

The counter-tariffs take effect on US goods from Sep 8 and will impose duties of 15 per cent, 25 per cent and 50 per cent across 700 products imported from south of the border, a government statement said.

In terms of financial support for affected workers and industries, Canada announced a C$7.5 billion package of new and enhanced measures including support for small and medium-sized businesses, a stream for funding cash flows of companies, and support for workers who could be at risk due to the new tariffs.

The new measures aim to support workers and businesses during "challenging times", Canada's government said late Monday.

Fresh 50 per cent US tariffs took effect on a range of Canadian goods Saturday, after trade negotiations collapsed the prior day at the eleventh hour.

The duties impact some US$20 billion in goods, or about 5.5 per cent of Canadian exports to the United States, economists estimate.

On Monday, Trump additionally pledged to double tariffs on Canadian autos starting next year, up to 50 per cent from the current 25 per cent for non-US content.

Ontario Premier Doug Ford criticised Trump's tariff threat on autos, saying he could "kiss my ass" and threatening an electricity export surcharge.

In an earlier phase of the dispute, Ontario imposed a temporary 25 per cent surcharge on electricity exports to three US states.

Trump has since lashed out at Ford online, warning of "far worse" consequences.

He also referred to the Canadian prime minister as a "governor", re-upping his inflammatory push for Canada to become the 51st US state.

Highlighting the animosity, Trump on Tuesday said he was considering renaming Lake Ontario as "Lake America", as he did last year with the Gulf of Mexico.

The latest tariffs Trump imposed will raise the US effective tariff rate on Canadian exports to 6.9 per cent from 5.1 per cent, Oxford Economics estimates.

Tariffs on plastics, electrical machinery, and wood and paper products contribute the most to the increase.

"Manufacturers in Quebec, New Brunswick, and Ontario will be affected the most," Oxford Economics said.

– with Agencies inputs --