Stocks fell into a freefall Monday — suffering their worst day of the year as China retaliated against President Trump’s recent tariff threats.

The Dow Jones Industrial Average plunged by more than 950 points in afternoon trading as China delivered a one-two punch to the US — first by allowing its currency to sink to an 11-year low against the US dollar, and then by halting imports of US crops.

The blue-chip index settled down 767.27 points — or 2.9 percent — at 25,717.74 — marking its steepest drop of the year on a points basis, and the sixth biggest drop in the Dow’s 123-year history, also based on points fallen.

The S&P 500 and the Nasdaq also suffered their worst drops of 2019, with the S&P closing down 2.98 percent to close at 2,844.75, and the Nasdaq ending the day off 3.47 percent to 7,726.04.

Monday’s sell-off was spurred by China allowing the yuan to fall below the 7-per-dollar level for the first time in more than a decade — a move that makes Chinese imports cheaper and arguably gives them an unfair trade advantage.

“It’s called ‘currency manipulation,’” Trump said in a tweet Monday. “Are you listening Federal Reserve? This is a major violation which will greatly weaken China over time!”

The 1.4 percent drop in the yuan comes just days after Trump angered China with plans to tax $300 billion of Chinese imports at 10 percent starting next month.

China pulled the moves in an effort to show that it, too, has financial ammunition it can use in the burgeoning trade battle, experts said.

“They can make it much more difficult for US companies to sell goods and services in China,” Quincy Krosby, chief market strategist at Prudential Financial, told The Post.

Indeed, adding to rising tensions Monday, China’s Commerce Ministry said that Chinese companies have stopped buying US crops — and that the nation could impose farm tariffs next.

“Any hopes of a quick resolution with China are fading quickly,” Ryan Detrick, senior market strategist at LPL Financial, said Monday.

Apple, which makes its popular iPhone in China, was one of the weakest stocks on the Dow, falling more than 5.2 percent to close at $193.34 a share. Caterpillar and Boeing, which both rely heavily on business in China, saw their shares fall 2.3 percent and 2.5 percent respectively on renewed trade tensions.

After markets closed, Trump’s Treasury Secretary Steve Mnuchin officially labeled China a currency manipulator. The designation that carries no immediate punishment but could rattle markets further Tuesday.

The Dow’s worst point drop was just 18 months ago when the Dow fell 1,175.21 points on Feb. 5, 2018. At the time, traders worried massive stock gains and higher-than-expected wage growth would force the Federal Reserve to hike rates to prevent the economy from overheating.

Now the market finds itself in a different dynamic with the Fed cutting rates to maintain the economic expansion and the US deeply embroiled in spats with its trading partners.