The new levies on cars and light trucks will take effect on April 3, the day after Trump plans to announce reciprocal tariffs aimed at the countries responsible for the bulk of the US trade deficit.
They come on top of duties already introduced on steel and aluminum, and on goods from Mexico, Canada and China.
The US imported $US474 billion ($A751 billion) worth of automotive products in 2024, including passenger cars worth $US220 billion ($A348 billion).
Mexico, Japan, South Korea, Canada and Germany were the biggest suppliers.
European Commission President Ursula von der Leyen described the move as "bad for businesses, worse for consumers", while Canadian Prime Minister Mark Carney labelled the tariffs a "direct attack" on Canadian workers and said retaliatory measures were being considered.
"We will defend our workers, we will defend our companies, we will defend our country, and we will defend it together," Carney told reporters in Ottawa.
Automakers Toyota Motor and Mazda Motor led declines in stocks in Japan, which relies on autos for more than a quarter of its exports to the US.
Shares of automakers in South Korea, Hyundai Motor and Kia Corp, also fell sharply.
Japanese Prime Minister Shigeru Ishiba said Tokyo would put "all options on the table" in dealing with the new tariffs.
Brazil's President Luiz Inacio Lula da Silva said Trump risked damaging the US economy with additional tariffs.
"It will raise the prices of goods and could lead to inflation that he hasn't yet realised," Lula told reporters in Tokyo on Thursday.
"Protectionism doesn't help any country in the world," he said, vowing to lodge a complaint with the World Trade Organisation over a trade levy on Brazilian steel.
Trump sees tariffs as a tool to raise revenue to offset his promised tax cuts and to revive a long-declining US industrial base.
Many trade experts, however, expect prices to initially rise and demand to fall, hurting a global auto industry that is already reeling from uncertainty caused by Trump's rapid-fire tariff threats and occasional reversals.
"We're going to charge countries for doing business in our country and taking our jobs, taking our wealth, taking a lot of the things that they've been taking over the years," Trump said at the Oval Office on Wednesday.
The United Auto Workers, long-standing critics of free trade agreements it says have destroyed American jobs, lauded the move.
"These tariffs are a major step in the right direction for auto workers and blue-collar communities across the country, and it is now on the automakers, from the Big Three to Volkswagen and beyond, to bring back good union jobs to the US," group president Shawn Fain said in a statement.
Shares of US automakers, which are highly integrated with plants and suppliers in Canada and Mexico, fell in after-hours trading.
Brad Setser, a former US Treasury official now with the Council on Foreign Relations, said some four million cars from Canada and Mexico faced 25 per cent or more tariffs, which would likely drive up prices and dampen US car sales for "a while".
The Center for Automotive Research said the new levies were expected to cost car buyers thousands of dollars more, hitting new vehicle sales and resulting in job losses since the US automotive industry relied heavily on imported parts.
Trump's directive included temporary exemptions for auto parts while government officials sort through the complexities of turning his proclamation into practice.
Since taking office on January 20, Trump has announced and delayed tariffs on Canada and Mexico for what he alleges is their role in allowing the opioid fentanyl into the US; set import taxes on goods from China for the same reason; launched hefty duties on imports of steel and aluminum; and has repeatedly touted his plans to announce global reciprocal tariffs on April 2.
Trump said on Wednesday auto tariffs could be net neutral for Tesla, the electric car company led by Elon Musk, who is also spearheading a government cost-cutting effort.
Musk later posted on X that Tesla would not be unscathed.
"The tariff impact on Tesla is still significant," he wrote.
