WASHINGTON/OTTAWA/MEXICO CITY - US President Donald Trump said Monday that 25 percent tariffs on Mexico and Canada will take effect on Tuesday, March 4.

He told reporters at the White House it’s “very importantly” that the tariffs on Canada and Mexico will start Tuesday.

"What they have to do is build their car plants, frankly, and other things in the United States, in which case they have no tariffs," Trump said.

Trump also reiterated that the reciprocal tariffs will start on April 2.

READ MORE: US commerce chief: Trump to set exact levels for Mexico, Canada tariffs

On Feb 1, Trump signed an executive order to impose a 25 percent tariff on goods imported from Mexico and Canada, with a 10 percent tariff increase specifically for Canadian energy products.

On Feb 3, Trump announced that the additional tariffs on goods from Mexico and Canada would be deferred for one month, allowing more time for negotiations. According to this decision, the relevant tariff measures are set to take effect on March 4.  

Canadian Foreign Affairs Minister Mélanie Joly said Canada is ready to hit back at Trump's tariffs right away, local media reported.

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Joly on Monday said if the levies go into force, Ottawa will revive its previously announced plan for 25 percent retaliatory tariffs on 155 billion Canadian dollars ($107 billion) worth of American goods.

"We know this is an existential threat to us. There are thousands of jobs in Canada at stake. Now, we've done the work, we are ready, should the US decide to launch their trade war," Joly said.

Canadian officials made a month-long diplomatic push to avoid tariffs. Joly said Canada has responded to Trump's concerns about the border. Canada named a new "fentanyl czar" and listed Mexican cartels as terrorist groups but is still left waiting to see what happens next.

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Joly said she will meet with Prime Minister Justin Trudeau when he returns from London.

Natural Resources Minister Jonathan Wilkinson said Monday that Canada and the United States are no longer trade partners as before even if the tariffs are removed.

"I don't think we are going back there even if the tariffs are removed," said Wilkinson.

Meanwhile, Mexican President Claudia Sheinbaum called for "temperance, serenity and patience" as the US tariffs are set to be effective.

Addressing her daily morning press conference, Sheinbaum reassured the public that her administration has multiple backup plans in place should the tariffs be imposed.

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She said that recent meetings between Mexican and US security and trade officials "went very well".

"We will wait and see what happens. In this situation, we must have temperance, serenity and patience," she said.

Mexico has prepared "Plan A, Plan B, Plan C and Plan D", said the president, without providing further details.

While she did not rule out speaking directly with Trump, Sheinbaum emphasized that Mexico remains calm and prepared. "So whatever his decision is, we will make our decisions and there is a plan and there is unity in Mexico," she said.

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She also cautioned against speculation, stressing that the decision to impose tariffs ultimately rests with the US government.

Trump had previously agreed to delay a 25 percent tariff on Mexican goods for one month after Sheinbaum ordered the deployment of 10,000 National Guard troops to the US-Mexico border to curb drug trafficking and mass immigration.