■ Apple, for which China is a key market, tumbled more than 3 percent.

■ Selling was especially heavy among semiconductor stocks, as investors grappled with the prospect of the flow of crucial microchips to Huawei being cut off. The SOX index of semiconductor shares fell more than 4 percent. Qualcomm fell about 6 percent. Roughly two-thirds of Qualcomm’s sales come from China and Hong Kong.

■ The chip-centric sell-off was the latest indication that escalating economic tensions between China and the United States could upend the year’s stock market surge. Through the first four months of 2019, the S&P 500 was up 17.5 percent. But the benchmark index is down more than 3 percent in May.