China’s currency was also hit by selling. China keeps a tight grip on the value of its currency, but the small amount that is traded outside of its borders — the so-called offshore renminbi — weakened against the dollar.

The intensifying trade war adds to China’s challenges, including signs that its effort to tame its debt problems could slow economic growth. Investors have turned skittish as a result. China has now entered bear market territory — when prices drop by more than 20 percent from a peak — with its market hovering at levels not seen since a rout three years ago set off a domino effect in global trading.

The Trump administration promised Tuesday night to impose tariffs on an additional $200 billion of Chinese products, including chemicals, handbags, petroleum and fish. That move came just days after the United States started levies on $34 billion worth of Chinese goods like robotics, ball bearings and even airplane parts.

The Chinese government pledged Wednesday that it would take unspecified countermeasures. It has matched previous tariffs dollar for dollar, leading some investors to worry that trade could get costlier still.

David French, an executive at the National Retail Federation, called the latest round of tariffs by the Trump administration a “reckless strategy that will boomerang back to harm U.S. families and workers.”