WASHINGTON >> President Donald Trump fired the biggest shot yet in the global trade war by imposing tariffs on $34 billion of Chinese imports, delivering on a promise to his political supporters that risks provoking retaliation and harming the world economy.

The duties on Chinese goods were due to start at 12:01 a.m. Friday in Washington, which is just after midday in China. Levies on another $16 billion of goods could follow in two weeks, Trump earlier told reporters, before suggesting the final total could eventually reach $550 billion, a figure that exceeds all of U.S. goods imports from China in 2017.

U.S. customs officials will begin collecting an additional 25 percent tariff on imports from China of goods ranging from farming plows to semiconductors and airplane parts. It’s the first time the U.S. has imposed tariffs directly aimed at Chinese goods following months in which Trump accused Beijing of stealing American intellectual property and unfairly swelling America’s trade deficit.

The riskiest economic gamble of Trump’s presidency could spread as it enters a new and dangerous phase by imposing direct costs on companies and consumers globally. China has vowed to hit back in kind on goods ranging from American soybeans to pork, which may in turn prompt Trump to raise trade barriers even higher.

“Once these tariffs start going into effect, it’s pretty clear the conflict is real,” said Robert Holleyman, former deputy U.S. trade representative under President Barack Obama and now a partner at law firm Crowell and Moring LLP. “If we don’t find an exit ramp, this will accelerate like a snowball going down a hill.”

Recent U.S. tariffs on steel and aluminum antagonized fellow developed nations and drew return fire from countries including the European Union and Canada.

Chinese state media has run numerous commentary pieces on the dispute over the past few days criticizing the American position.

As the world’s most developed nation and the rule-maker of the current global governing system, there is “astounding absurdity” in the U.S. complaining that it’s been bullied in trade, the People’s Daily, the flagship newspaper of the Communist Party of China, said in a Chinese language commentary on Friday.

Some other media were more circumspect, with the English-language China Daily calling on China to be confident but not arrogant. The Global Times, an English tabloid under the People’s Daily, warned that China should be prepared for the U.S. to try to contain China’s rise.

Iconic American companies such as Harley-Davidson Inc. are among those set to suffer. The motorcycle maker said this month it may move production out of the U.S. to avoid EU tariffs on its bikes. American businesses from Apple Inc. and Walmart Inc. to General Motors Co. all operate in China and are keen to expand. That hands Chinese President Xi Jinping room to impose penalties such as customs delays, tax audits and increased regulatory scrutiny if Trump delivers on his threat of bigger duties on Chinese trade.

Chinese stocks have taken a beating in recent weeks, entering a bear market, as concerns about the trade war have mingled with worries about China’s ability to control its debt and maintain growth. U.S. stocks are up slightly more than 2 percent this year as investors have weighed the threat of trade frictions against the strong performance of the U.S. economy.

Trump is doubling down on his promise to put “America First” in the nation’s foreign and economic policies. He blames China for a bilateral trade deficit of $336 billion and for costing U.S. manufacturing jobs.

Politically, the get-tough-on-China campaign is aimed at helping score points with the voters who propelled Trump to the White House even though some members of his Republican party — particularly those in farming states that could be hit by retaliation — urged a retreat. Failure that brings economic pain could cost Republican seats in November’s mid-term elections.

As a candidate in 2016, Donald Trump won support with a promise to redress an unbalanced trade relationship with the rest of the world. In the White House in 2018, he has started to make good on that pledge. Bloomberg Economics’ base case remains more trade skirmish than trade war, but the risks are increasing.

The tariffs could jeopardize an economic upswing that has extended to nine years on his watch and pushed the jobless rate to the lowest in nearly half a century. U.S. and Chinese companies will now find it costlier to trade with each other, meaning less demand and higher prices. The International Monetary Fund warns an extended spat could undermine the strongest global expansion since 2011.

The extent of the economic damage will depend on how far both sides go. If the U.S. and China cool off after a first round of tariffs, the impact on their economies will be modest, according to Bloomberg Economics. Under a full-blown trade war in which the U.S. slaps 10 percent tariffs on all other countries and they respond, the economists reckon U.S. growth would slow by 0.8 percentage point by 2020.

The impact of the first round of tariffs on $34 billion in Chinese goods will be “quite small,” said Ethan Harris, head of global economic research at Bank of America Merrill Lynch. But he doesn’t “see the war ending until there are casualties.”

“This plays out over the next few months, until both sides start to feel a little pain and realize this isn’t a bloodless march to victory,” said Harris.

JPMorgan Chase & Co. economists warn the biggest risk may come from the indirect impact of tightening credit conditions and business confidence, reducing scope for investment and hiring while undermining financial markets.

Vehicles could be the next battleground. The Trump administration is reviewing whether to introduce duties on imported cars and trucks in a bid it says to protect U.S. national security. The threat deepened tensions with the EU, which warns that car tariffs would inflict pain across its 28 member states.

Trump argues that his approach will force other countries to trade more fairly, reducing America’s $552 billion trade deficit and prompting employers to return to America. But recent U.S. tax cuts and spending increases will probably buoy the dollar and the nation’s current-account deficit anyway, the IMF said this week.

America’s hawkish trade agenda may therefore not deliver the results the president is seeking.

That could set the stage for a prolonged conflict with Beijing, which has shown little interest in making fundamental changes to its economic model. Xi has balked at U.S. demands to stop subsidizing Chinese firms under his plan to make the nation a leader in key technologies by 2025. Negotiations between the two countries petered out with the Chinese accusing the U.S. of blackmail.

The U.S. imports much more from China than the other way around, giving the U.S. an advantage in a tariff dispute. That means Beijing could focus on introducing bigger regulatory or tax burdens on American companies who operate in China or want to tap its growing market. It could even take the drastic steps of devaluing the yuan or reducing its $1.2 trillion holdings of U.S. Treasuries, measures that would hurt it as well as the U.S.

In the past, the U.S. used its economic clout to win trade skirmishes with developing countries, said James Boughton, a senior fellow at the Centre for International Governance Innovation in Waterloo, Ontario. China, whose economy has grown tenfold since it joined the World Trade Organization in 2001, poses a much more formidable adversary.

“The dynamic is different from anything we’ve seen,” said Boughton. “China has an ability to ride out this kind of pressure, to weather the storm, that a lot of countries didn’t have in the past.”