Stocks plunged, sending the Dow Jones industrials down more than 700 points, as investors feared that trade tensions will spike between the U.S. and China.

The Dow plummeted 724 points, or 2.9%, underlining mounting concerns among investors about looming tariffs on China. It was the fifth-largest point decline in history and the market's worst day since the extreme turmoil of early February. 

The S&P 500 dropped 2.5% and the Nasdaq 2.4%.

There are fears China will retaliate against major U.S. industries from agriculture to airplane manufacturing. For instance, China is a major market for Boeing, which makes more than half of all commercial jetliners operating in that country. The United States exported more than 30 million tons of soybeans — worth more than $10 billion — to China last year.​

Beijing warned on Thursday it will "certainly take all necessary measures to resolutely defend" itself. China didn't specify how it will respond, but U.S. crops like soybeans are likely to be in the crosshairs.