WASHINGTON — President Donald Trump has  directed the U.S. Trade Representative to prepare new tariffs on $200 billion in Chinese imports as the two nations move closer to a trade war.

In response, China has threatened what it called “comprehensive measures,” raising the risk that it would target major American companies operating in China.

Trump’s proposed new tariffs would amount to the latest round of punitive steps in an escalating rift between the world’s two largest economies.The White House has accused China of forcing U.S. companies to share advanced technology with Chinese partners as a condition of doing business there.

Trump previously ordered 25 percent tariffs on $50 billion in Chinese goods in retaliation for Beijing’s forced transfer of U.S. technology and for intellectual property theft. Those tariffs were matched by China’s threat to penalize on U.S. exports, a move that drew the president’s ire.

The tit-for-tat tariffs could then escalate further yet: Trump threatened tariffs on $200 billion more in Chinese products if Beijing lashes back again.

Combined, the potential tariffs on Beijing could reach $450 billion — an amount equal to 89 percent of Chinese goods imported to the United States last year.

Neither side has yet imposed tariffs on the other in their growing dispute over technology and the U.S. trade gap; the first round is to take effect on July 6.     The president asserted in a statement Monday night that China is determined “to keep the United States at a permanent and unfair disadvantage.”

U.S. stock markets fell sharply Tuesday, with investors increasingly nervous about the impact of the escalating fight. The Dow Jones industrial average was down about 320 points, or 1.3 percent. Shares of large U.S. companies with significant overseas business were hit especially hard. Boeing’s stock shed 3.6 percent, Caterpillar 3.7 percent and GE 1.7 percent.

China might be unable to match the U.S. tariffs because it imports much less from the United States — $130 billion in goods last year, compared with Chinese exports to the United States of $505.5 billion. That would leave less than $100 billion in U.S. goods to subject to a tariff hike, far short of the $200 billion Trump is threatening.

Oxford Economics estimates that if Trump imposed the $200 billion in duties and China responded in kind, U.S. growth could slow by 0.3 percentage point next year.

In the first round of penalties announced by both nations, to take effect July 6,  the U.S. plans to impose tariffs of 25 percent on $34 billion of Chinese imports, such as construction machinery, aerospace and power generation equipment. The White House is finalizing a list of $16 billion in additional goods it will sanction later.

China is retaliating by raising import duties on $34 billion worth of American goods. They include electric cars, whiskey and soybeans — a politically and economically vital export of America’s heartland, where Trump enjoys support. And Beijing says it would impose tariffs on $16 billion more if the United States does so, too.

The tariffs on Chinese imports are the latest in a spate of protectionist measures unveiled by Trump in recent months. They included tariffs on steel and aluminum imports and a combative stance on trade negotiations from North America to Asia.

Wall Street has viewed the trade tensions with rising concern that they could strangle the economic growth achieved during Trump’s watch. Gary Cohn, Trump’s former top economic adviser, said last week that a “tariff battle” could result in price inflation and consumer debt — “historic ingredients for an economic slowdown.”