Markets around the world shuddered on Thursday after President Trump announced across-the-board 10 percent tariffs on all U.S. trading partners except Canada and Mexico, as well as even higher tariffs on dozens of America’s other main trading partners.

Futures on the S&P 500, which allow investors to trade the index outside normal trading hours, slumped over 3 percent. Asian markets fell sharply, with benchmark indexes dropping more than 3 percent in Japan, and nearly 2 percent in Hong Kong and South Korea.

The slide came after Mr. Trump, speaking at a ceremony at the White House on Wednesday, announced a new 10 percent base line tariff on all imports as well as country specific taxes on goods from a host of other countries. Those included a 34 percent tax on Chinese imports, on top of 20 percent in tariffs he recently put on China, and 20 percent on goods coming from the European Union and 24 percent on Japanese imports.

The initial market reaction suggested that the scale of the tariffs on Wednesday had come as a surprise, and analysts were still trying to figure out how the figures had been derived.

“I think the numbers are shockingly high compared to what people were expecting and it is inexplicable in many ways,” said Peter Tchir, head of macro strategy at Academy Securities. “I think it’s a disaster.”

The administration had adjusted its estimates of the tariffs imposed on the United States to include adjustments for what it deemed currency manipulation or even other taxes, with analysts questioning the analytical basis for doing so.

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