Prime Minister Justin Trudeau slammed Donald Trump's sweeping tariffs on Canada, calling it a "very dumb thing to do" and vowed to conduct a "relentless fight" to protect its economy.

Trump has imposed 25% tariffs on products entering the US from Canada and Mexico, and has increased a levy on goods coming from China.

The Canadian prime minister announced retaliatory tariffs on US exports and warned that a trade war would be costly for both countries.

But Trump pushed even further in a post on Truth Social, saying: "Please explain to Governor Trudeau, of Canada, that when he puts on a Retaliatory Tariff on the U.S., our Reciprocal Tariff will immediately increase by a like amount!"

Trudeau accused the US president of planning "a total collapse of the Canadian economy because that will make it easier to annex us".

"That is never going to happen. We will never be the 51st state," he told reporters on Tuesday.

"This is a time to hit back hard and to demonstrate that a fight with Canada will have no winners."

He said that Canada's main goal remains to get the tariffs lifted so that they "don't last a second longer than necessary".

Trump said he is protecting US jobs and manufacturing, and trying to prevent illegal migration and drug trafficking.

The US president said his goal is to clamp down on the powerful opioid fentanyl; he has variously blamed the other countries for the drug's arrival in the US.

Responding to the accusations, Trudeau said on Tuesday there was "no justification" for the new tariffs, because less than 1% of the fentanyl intercepted at the US border comes from Canada.

Trudeau's words were echoed by Mexican President Claudia Sheinbaum, who said there was "no motive, no reason, no justification" for Trump's move. Speaking on Tuesday, she too vowed to issue her own "tariff and non-tariff measures" - but said further details would be given on Sunday.

Experts said Trump's tariffs are likely to push up prices for consumers in the US and abroad.

The three countries targeted are America's top trading partners, and the tit-for-tat measures also prompted fears of a wider trade war.

Tariffs are a tax on imports from other countries, designed to protect against cheaper competition from elsewhere, and boost businesses and jobs at home.

Canada's retaliatory measures include a 25% reciprocal tariff that will be imposed on C$155bn (US$107bn; £84bn) of American goods:

• A tariff on C$30bn worth of goods will become effective immediately
• Tariffs on the remaining C$125bn of American products will become effective in 21 days' time

Canada's Immigration Minister Marc Miller warned that as many as a million jobs in Canada were at risk if the tariffs were implemented, given how intertwined trade was between the two countries.

"We can't replace an economy that is responsible for 80% of our trade overnight and it's going to hurt," he said on Monday.

Speaking to the AFP news agency, a car manufacturing employee in the Canadian province of Ontario said people were indeed "pretty scared" of being laid off. "I just bought my first house," Joel Soleski said. "I might have to look for work elsewhere."

The sector is one that could be badly affected by the new tariffs regime in North America. Car parts may cross US-Canada border several times during the manufacturing process, and so might be taxed on multiple occasions.

Ontario Premier Doug Ford, whose province is home to Canada's auto manufacturing industry, told reporters on Tuesday that he anticipates assembly plants will "shut down on both sides of the border" as a result of the tariffs.