US President Donald Trump ignited a potentially ruinous trade war Wednesday as he slapped sweeping 10 percent tariffs on imports from around the world and harsh additional levies on key trading partners.

Speaking in the White House Rose Garden against a backdrop of US flags, Trump unveiled particularly stinging tariffs on China and the European Union on what he called "Liberation Day."

Trump's tariffs triggered immediate anger, with US ally Australia blasting them as "unwarranted" and Italy calling them "wrong," while other countries have already vowed retaliation.

"For decades, our country has been looted, pillaged, raped and plundered by nations near and far, both friend and foe alike," Trump said.

Wall Street was closed when Trump made his announcement but the S&P index was down 1.5 percent in after-hours trading. The dollar fell one percent against euro as he was speaking, but then recovered.

Trump reserved some of the heaviest blows for what he called "nations that treat us badly," including 34 percent on goods from superpower rival China, 20 percent the European Union and 24 percent on Japan.

But the 78-year-old Republican — who held up a chart with a list of the biggest levies — said that he was "very kind" and so was only imposing half the amount that the "worst offenders" taxed US exports.

'Make America wealthy again'

For the rest, Trump said he would impose a "baseline" tariff of 10 percent, including another key ally, Britain.

An audience of cabinet members, as well as workers in hard hats from industries including steel, oil and gas, whooped and cheered as Trump said the tariffs would "make America wealthy again."

"This is Liberation Day," Trump said, adding that it would "forever be remembered as the day American industry was reborn."

Sweeping auto tariffs of 25 percent that Trump announced last week are also due to take effect at 12:01 AM (0401 GMT) Thursday.

Canada and Mexico are not affected by the new tariffs as Trump has already imposed levies on the two US neighbors for what he says is their failure to crack down on trafficking of the drug fentanyl.

Trump had telegraphed the move for weeks, insisting tariffs will keep the United States from being "ripped off" by other countries and spur a new economic "Golden Age."

But many experts warn the tariffs risk triggering a recession at home as costs are passed on to US consumers, and a damaging trade war abroad.

US Treasury Secretary Scott Bessent warned nations not to impose countermeasures, saying on Fox News: "If you retaliate, there will be escalation."

The world has been on edge ahead of Trump's announcement, and his tariffs hit countries all over the globe.

Some of the worst hit were in Asia, including 49 percent for Cambodia, 47 percent for Vietnam and 44 percent for military-ruled Myanmar, which was recently hit by a devastating earthquake.

One country attracting the highest rate of 50 percent was Lesotho — the southern African nation that Trump recently called a country "nobody has ever heard of."

'Totally unwarranted'

The tariffs will also reinforce fears that Trump is backing even further away from US allies towards a new order based on a vision of American supremacy.

Australian Prime Minister Anthony Albanese on Thursday said the tariffs were "totally unwarranted" and would change the perception of the relationship with the United States.

Italian Prime Minister Giorgia Meloni, a close Trump ally, said the levies on the EU were "wrong" but pledged to work with Washington for a deal.

Britain escaped relatively lightly after a diplomatic offensive that included Prime Minister Keir Starmer turning up to the White House with an invitation from King Charles III for a state visit.

But it remains committed to sealing a trade deal that could "mitigate" the 10 percent tariff it now faces, business minister Jonathan Reynolds said.

Trump has had a long love affair with tariffs, insisting in the face of experts that they are a cure-all for America's trade imbalances and economic ills.

The billionaire insists the levies will bring a "rebirth" of America's hollowed-out manufacturing capacity, and says companies can avoid tariffs by moving to the United States.