NEW YORK — U.S. stocks fell Wednesday after Nvidia warned new restrictions on exports to China will chisel billions of dollars off its results, while companies around the world said President Donald Trump’s trade war is clouding forecasts for how they and the economy will do this year.

The S&P 500 sank 2.2% after falling as much as 3.3% earlier. Such an amount would have vied for one of its worst losses in years before the historic, chaotic swings that have upended Wall Street in recent weeks.

The Dow Jones Industrial Average dropped 699 points, or 1.7%, and the Nasdaq composite sank a market-leading 3.1%.

Losses accelerated after the head of the Federal Reserve said again that Trump’s tariffs appear to be bigger than it expected, which could in turn slow the economy and raise inflation more than it had earlier thought. But Jerome Powell also said again that the Fed will need more time before deciding whether to lower interest rates, which could help the economy but make inflation worse, or to do the opposite.

“All of this is highly uncertain,” Powell said. “We’re thinking now, really before the tariffs have their effects, (about) how they might affect the economy. That’s why we’re waiting really to see what the policies ultimately are, and then we can make a better assessment of what the economic effects will be.”

Some companies are already seeing big effects because of changes from Washington.

Nvidia dropped 6.9% after it said the U.S. government is restricting exports of its H20 chips to China, citing worries that they could be used to build a supercomputer. The restrictions could mean a hit of $5.5 billion to Nvidia’s results for the first quarter, covering charges related to inventory and purchase commitments.

Advanced Micro Devices sank 7.3% after it said U.S. limits on exports to China for its own chips may mean a hit of up to $800 million for inventory and other charges.

In Amsterdam, ASML’s stock sank 5.2%. The Dutch company, whose machinery makes chips, said demand for artificial-intelligence technology is continuing to drive growth.