A monthslong calm on Wall Street shattered Friday, and U.S. stocks tumbled after President Donald Trump threatened to crank tariffs much higher on China.

The S&P 500 sank 2.7% in its worst day since April. The Dow Jones Industrial Average dropped 878 points, or 1.9%, and the Nasdaq composite fell 3.6%.

Stocks had been heading for a slight gain in the morning, until Trump took to his social media platform and said he’s considering “a massive increase of tariffs” on Chinese imports.

He’s upset at restrictions China has placed on exports of its rare earths, which are materials that are critical for the manufacturing of everything from consumer electronics to jet engines.

“We have been contacted by other Countries who are extremely angry at this great Trade hostility, which came out of nowhere,” Trump wrote on Truth Social.

He also said “now there seems to be no reason” to meet with China’s leader, Xi Jinping, after earlier agreeing to do so as part of an upcoming trip to South Korea.

The ratchet higher in tensions between the world’s largest economies led to widespread drops across Wall Street, with roughly six out of every seven stocks within the S&P 500 falling.

Nearly everything weakened, from Big Tech companies like Nvidia and Apple to stocks of smaller companies looking to get past uncertainty about tariffs and trade.

The market may have been primed for a slide. U.S. stocks were already facing criticism that their prices had shot too high following the S&P 500’s nearly relentless 35% run from a low in April.

The index, which dictates the movements for many 401(k) accounts, is still near its all-time high set earlier in the week.