US President Donald Trump is expected to announce new tariffs against Canada and Mexico that will begin on March 1 but will include a process for the countries to seek specific exemptions for certain imports, three people familiar with the planning told Reuters.

The tariff situation remained fluid on Friday and no decision is final until Trump makes a public announcement.

The sources, who asked not to be named because they are not authorised to speak publicly on the matter, said they did not have details on a final tariff rate, but noted Trump has consistently said that he plans to impose a 25 per cent tariff on imports from the two countries on Saturday.

Separately, an administration official said Trump was reviewing tariff plans today which may allow for some exemptions. Still, any exemptions would be “few and far between”, the official said.

While the announcement of tariffs may roil financial markets and strain the US relationship with its top two trading partners, offering a 28-day window before implementation and a process for exemptions would suggest a more careful approach by the Trump administration.

It also would buy time for negotiations over actions by Canada and Mexico to meet Trump’s stated goals for the duties, to pressure the two US neighbours to halt the flow of illegal immigrants and deadly fentanyl across the US border.