US President Donald Trump says the sweeping tariffs he has imposed on products from Mexico, Canada and China might cause "short-term" pain for Americans as global stock markets tumble on concerns the levies will spark an economically damaging trade war.
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Trump said he would talk on Monday with the leaders of Canada and Mexico, which have announced retaliatory tariffs of their own, but downplayed expectations they would change his mind.
"I don't expect anything dramatic," Trump told reporters as he returned to Washington from his Mar-a-Lago estate in Florida.
"They owe us a lot of money, and I'm sure they're going to pay."
He said tariffs on the European Union would go ahead, but did not say when.
European leaders meet in Brussels on Monday and are expected to discuss tariffs in the wake of Trump's comments.
"It will definitely happen with the European Union. I can tell you that because they've really taken advantage of us," Trump told reporters on Sunday.
"They take almost nothing and we take everything from them."
The tariffs on Canada, Mexico and China, outlined in three executive orders, are due to take effect on Tuesday (4pm AEDT).
Economists said the plan to impose 25 per cent tariffs on Canada and Mexico and 10 per cent tariffs on China - the US's three largest trading partners - would slow global growth and drive prices higher for Americans.
Trump says they are needed to curb immigration and narcotics trafficking and spur domestic industries.
Financial market reaction to US tariffs is reflecting concerns about the fallout from a trade war. (AP PHOTO)
"We may have short-term some little pain, and people understand that. But long term, the United States has been ripped off by virtually every country in the world," he said.
Financial market reaction on Monday reflected concerns about the fallout from a trade war, with US stock futures falling about two per cent.
Shares across Asia, including Tokyo, Seoul and Sydney also slid about two per cent.
The Chinese yuan, Canadian dollar and Mexican peso all slumped against a soaring dollar.
With Canada and Mexico the top sources of US crude oil imports, US oil prices jumped more than $US1, while petrol futures rose almost three per cent.
North American companies braced for new duties that could up-end industries from autos to consumer goods to energy.
Trump's tariffs will cover almost half of all US imports and require the US to more than double its own manufacturing output to cover the gap, ING analysts wrote.
Mexican President Claudia Sheinbaum has accused the US of failing to tackle its fentanyl problem. (AP PHOTO)
"Economically speaking, escalating trade tensions are a lose-lose situation for all countries involved," they wrote in a note on Sunday.
Other analysts said the tariffs could throw Canada and Mexico into recession and usher in "stagflation" - high inflation, stagnant economic growth and elevated unemployment - at home.
Goldman Sachs economists said the levies were likely to be temporary but the outlook was unclear because the White House set very general conditions for their removal.
Trump vowed to keep them in place until what he described as a national emergency over fentanyl, a deadly opioid, and illegal immigration to the US ends.
China has said it would challenge the tariffs at the World Trade Organization and take other countermeasures but left the door open for talks with the US.
Its sharpest pushback was over fentanyl.
"Fentanyl is America's problem," China's foreign ministry said, adding that China has taken extensive measures to combat the problem.
Mexican President Claudia Sheinbaum, raising her fist in the air in a speech outside the capital, vowed resilience.
Prime Minister Justin Trudeau urged Canadians to boycott the United States and its goods. (AP PHOTO)
She accused the US of failing to tackle its fentanyl problem and said it would not be solved by tariffs.
Sheinbaum said she would provide more details on Monday of the retaliatory tariffs she ordered at the weekend.
Canada said on Sunday it would take legal action under the relevant international bodies to challenge the tariffs.
Prime Minister Justin Trudeau also encouraged Canadians to boycott their longtime ally after ordering retaliatory tariffs against $US155 billion ($A252 billion) of US goods, from peanut butter, beer and wine to lumber and appliances.
Trade lawyers said Trump could face legal challenges for testing the limits of US laws as some Republicans criticised his action.
"It will be paid for by American consumers," Republican Senator Mitch McConnell said in an interview on CBS's 60 Minutes.
Investors were considering the effects of additional tariffs promised by Trump, including those related to oil and gas, as well as steel, aluminium, semiconductor chips and pharmaceuticals.
A European Commission spokesperson said the EU "would respond firmly to any trading partner that unfairly or arbitrarily imposes tariffs on EU goods".
Australian Associated Press