After weeks of uncertainty surrounding his threats, Trump on Saturday signed off on broad 25-percent tariffs on Mexico and Canada -- despite a regional free trade pact -- while hitting China with a 10-percent tariff in addition to levies already in place.

The announcement capped an extraordinary second week of Trump's new term, with the president facing the worst US aviation disaster in over a decade as his administration moved to drastically overhaul the government in actions decried by critics as illegal.

China, Mexico and Canada are the top three US trade partners and all have vowed to retaliate when the tariffs take effect Tuesday.

"Will there be some pain? Yes, maybe (and maybe not!)" Trump wrote Sunday morning in all-caps on his Truth Social media platform.

"But we will Make America Great Again, and it will all be worth the price that must be paid."

Analysts expect the trade war to slow US growth and increase prices, at least in the short term, something the president had resisted acknowledging after frustration over rising costs was seen as a major factor in his November 2024 election win.

Seeking to limit a spike in fuel prices, Trump has put the levy on energy imports from Canada at only 10 percent.

The president in his order cited illegal immigration and the trafficking of the deadly opioid fentanyl as reasons for the "emergency" measures.

But on Sunday he also expressed general outrage at trade deficits, which he has long viewed as signs of unfair treatment against the United States.

"The USA has major deficits with Canada, Mexico, and China (and almost all countries!), owes 36 Trillion Dollars, and we're not going to be the 'Stupid Country' any longer," he wrote.

The Wall Street Journal, whose right-leaning editorial board complained Friday that Trump was launching "The Dumbest Trade War in History," was "working hard to justify... the decades long RIPOFF OF AMERICA," Trump said.

The 78-year-old billionaire on Sunday visited one of his golf courses in Florida, where he traveled for a second weekend in a row since his White House return.

- '51st state' -

In a separate social media post, Trump took particular aim at Canada, repeating his call for America's northern neighbor to become a US state.

Claiming the United States pays "hundreds of billions of dollars to SUBSIDIZE Canada," Trump said that "without this massive subsidy, Canada ceases to exist as a viable Country."

"Therefore, Canada should become our Cherished 51st State," he said, reiterating the expansionist threat against one of his country's closest allies.

The US Census Bureau says the 2024 trade deficit in goods with Canada was only $55 billion.

Canadian Prime Minister Justin Trudeau vowed Saturday to hit back with 25 percent levies on select American goods worth Can$155 billion (US$106.6 billion), with a first round on Tuesday followed by a second one in three weeks.

Leaders of several Canadian provinces have already announced retaliatory actions as well, such as the immediate halt of US liquor purchases.

The White House has not publicly announced what specific actions the countries could take to lift the tariffs.

"It's hard to know what more we can do, but we're obviously open to any other suggestions that come our way," Canada's ambassador to the United States Kirsten Hillman told ABC News on Sunday.

Trudeau, who flew to Florida to meet with Trump shortly after the November US election, said his attempts to speak again with Trump since his January 20 inauguration have been to no avail.

- Federal overhaul -

Mexican President Claudia Sheinbaum meanwhile said she had directed her economy minister to "implement Plan B," which includes yet-unspecified "tariff and non-tariff measures."

The European Union, which Trump has also vowed to hit with tariffs, said Sunday it would "respond firmly."

The drastic trade actions follow similarly sharp efforts by Trump's administration to quickly overhaul the federal government in his first two weeks.

Major actions have included the attempted dismissal of swaths of officials and a chaotic funding freeze that was halted in court and later walked back by the White House.

Trump's close ally Elon Musk, the world's wealthiest person, and his so-called Department of Government Efficiency were also pursuing efforts that were not fully clear, including reported efforts to probe federal payment and e-mail systems.

The tumult in the federal government coincided with the collision of an army helicopter and an airliner that killed 67 people in the US capital, the most deadly commercial airline crash since 2009.

Trump, addressing the crash on Thursday, pointed the finger at diversity programs.