President Trump unveiled his most expansive tariffs to date in a ceremony at the White House on Wednesday afternoon, saying he would impose a 10 percent tariff on all trading partners as well as double-digits tariffs on dozens of other countries that administration officials said had treated the United States unfairly.

Major trading partners including the European Union, China, Britain and India will also face higher “reciprocal” tariffs, based on trading practices that Mr. Trump deems unfair.

Under Mr. Trump’s plan, the United States will impose a staggering new 34 percent tariff on Chinese goods, on top of the 10 percent levy applied to imports from around the world and the 20 percent levy he already imposed on Beijing.

Some of Mr. Trump’s steepest rates apply to U.S. allies, including a 20 percent tariff on imports from the European Union and a 24 percent tariff on goods from Japan. India will face a 26 percent tariff on its exports to the United States.

White House officials said that pernicious trading practices by other countries had led to large and persistent trade deficits for the United States, and that other products, like lumber, copper, semiconductors, pharmaceuticals and critical minerals could face additional tariffs.

In a briefing with reporters, senior administration officials added they had little appetite for haggling over lower tariff rates, even with U.S. allies that have offered to reduce their own levies on American exports in recent days. They also issued an early warning to countries that have threatened to impose retaliatory tariffs against the United States.

Mr. Trump at one point described his approach as “kind,” explaining that the government would only be charging other countries half of the rate that they had calculated should be applied based on those countries’ trade practices. He framed his policies as a response to a national emergency, saying that tariffs were needed to boost domestic production.

“We’re going to start being smart, and we’re going to start being very wealthy again,” Mr. Trump said.

Mr. Trump had promised for months to impose the tariffs, which the president says will correct years of “unfair” trade in which other countries have been “ripping off” America.

Here’s what else to know:

• Markets stabilize: Stocks ended the day higher, rallying from earlier losses on a day shadowed by anticipation of Mr. Trump’s announcement of the tariff details. The S&P 500 closed 0.7 percent higher, while the tech-heavy Nasdaq Composite rose 0.9 percent. Tariff uncertainty drove sentiment on Wall Street in March, dragging the S&P 500 to its worst month since 2022.
• European response: European officials are poised to respond to Mr. Trump’s steel and aluminum tariffs with countermeasures. Although the bloc so far has concentrated on imposing higher tariffs on a wide variety of goods — whiskey, motorcycles and women’s clothing are among the products that could be affected — officials are also open to placing trade barriers on services, using a new trade weapon that was developed only in 2021 to target Big Tech and Wall Street.
• Tariff options: The administration has been weighing several different tariff strategies in recent weeks, including a 20 percent flat tariff on all imports, which Trump advisers have said could help raise more than $6 trillion in revenue for the U.S. government. Advisers have also discussed the idea of assigning different tariff levels to countries depending on the trade barriers those countries impose against American products, or exempting them from tariffs entirely through trade deals.
• Imported automobiles hit: New tariffs on automobiles made outside the United States go into effect on Thursday, adding to previous tariffs on steel, aluminum and other imports worth billions of dollars that Mr. Trump has imposed since returning to office in January.