U.S. stock futures were sinking again in premarket trading after massive U.S. tariffs against China kicked in overnight, followed by China retaliating with a huge tariff increase on U.S. imports. Oil prices tumbled to their lowest level in more than four years and a huge sell-off in U.S. Treasurys sent bond yields soaring.

Futures for the S&P 500 fell 2% before the bell to 4,914.50. If those losses hold and the index closes below 4,915.32, it will be in what investors call a bear market.

Futures for the Dow Jones Industrial Average slid 2.4% and Nasdaq futures slumped 1.8%.

In contrast to the rest of the world, markets in China reversed toward small gains Wednesday after that country responded with an 84% tariff on U.S. goods, in retaliation for U.S. President Donald Trump’s 104% tariffs on the world’s second-largest economy that went into effect at midnight Wednesday.

Beijing also added an array of countermeasures after Trump’s massive tariffs on China kicked in.

“If the U.S. insists on further escalating its economic and trade restrictions, China has the firm will and abundant means to take necessary countermeasures and fight to the end,” the Ministry of Commerce wrote in a statement introducing its white paper on trade with the U.S.

Massive share buybacks by big state-run investment funds and other state companies that often are instructed to support Chinese markets in times of crisis helped boost stock prices.

Hong Kong’s Hang Seng rose 0.7%, while the Shanghai Composite index closed 1.3% higher.

Prices for U.S. crude oil skidded more than 5% to $56.38 per barrel, their lowest level since the February of 2021 when the U.S. and global economies were still emerging from the COVID-19 pandemic. Rapidly falling oil prices often signal investor pessimism about economic growth and can signal a recession ahead.

Brent crude, the European standard, gave back $3.29 to $59.53 per barrel.

A sell-off in long-term U.S. Treasurys compounded the gloom around Trump’s tariffs and the damage they’re expected to cause the global economy. The yield on the 10-year Treasury — normally considered a safe haven during volatile equity markets — jumped 17 basis points to 4.44% early Wednesday.

Delta Air Lines pulled its guidance for 2025 Wednesday as the trade war scrambles expectations for business and household spending and depresses bookings across the travel sector.

“With broad economic uncertainty around global trade, growth has largely stalled,” CEO Ed Bastian said in a statement on Wednesday. “In this slower-growth environment, we are protecting margins and cash flow by focusing on what we can control.”

Even though the airline’s profit for the most recent quarter came in better than Wall Street expected, Delta shares were mostly unchanged in premarket trading.

The airline sector has been battered this year as investors, anticipating rising tariffs, put their money elsewhere. Shares are down 41% this year for the nation’s most profitable airline, which is better than rivals American and United.

Shares of pharmaceutical companies were also hit hard in off-hours trading after Trump said Tuesday night that he plans tariffs on pharmaceuticals so that more medications would be made in the U.S.

Pfizer and Merck each lost more than 4%. Most other big drugmakers were down between 2% and 4%, including Johnson & Johnson, Bristol Myers Squib and Eli Lilly.

The escalating global trade war — particularly between the U.S. and China — has sent markets careening this year with uncertainty about how the global economy would hold up to America’s new isolationist trade policy.

Analysts predict that markets will have more swings up and down given uncertainty over how long Trump will keep the stiff tariffs on imports, which will raise prices for U.S. shoppers and slow the economy. If they persist, economists and investors expect them to cause a recession. If Trump lowers them through negotiations relatively quickly, the worst-case scenario might be avoided.

Hope still remains on Wall Street that negotiations may be possible, which helped drive the morning’s rally. Trump said Tuesday that a conversation with South Korea’s acting president helped them reach the “confines and probability of a great DEAL for both countries.”

Trump’s trade war is an attack on the globalization that’s shaped the world’s economy and helped bring down prices for products on store shelves but also caused manufacturing jobs to leave for other countries. Trump has said he wants to narrow trade deficits, which measure how much more the United States imports from other countries than it sends to them as exports.

Markets in Europe also extended their losses, with Germany’s DAX sliding 4.1%. In Paris, the CAC 40 declined 3.9% and Britain’s FTSE 100 gave up 3.8%.

Elsewhere, markets remained gloomy. Japan’s Nikkei 225 closed 3.9% lower, at 31,714.03 and Prime Minister Shigeru Ishiba convened a meeting of top financial ministers to reiterate his call for them to do what they can to mitigate the damage from tariffs to Japanese automakers and other manufacturers.

Taiwan led the losses in Asia, as its Taiex plunged 5.8%. Big Tech industries were among the biggest decliners. Computer chip giant TSMC Corp. dropped 3.8% while iPhone maker Hon Hai Precision Industry plunged 10%.

In India, the Sensex declined 0.5% as the central bank cut its benchmark interest rate, while Bangkok’s SET shed 0.8%.

South Korea’s Kospi lost 1.7% to 2,293.70, and the government said it would provide help for its beleaguered automakers. The S&P/ASX 200 in Australia declined 1.8% to 7,375.00. Shares in New Zealand also fell.