Oil prices fall below $100 a barrel as China’s Covid-19 outbreak threatens demand.

Oil prices dropped, falling below $100 a barrel, as China, the world’s largest oil importer, imposed new lockdowns to combat an outbreak of Covid-, moves that could threaten demand.

The swing in oil prices, which were approaching $130 a barrel earlier this month, reverberated through the stock market: Shares of airlines rallied, and oil producers slid.

Brent crude, the global benchmark, fell about 8 percent to about $98.87 a barrel, its lowest price since late February. West Texas Intermediate crude, the U.S. benchmark, was down more than 8 percent at $94.43 a barrel. Over the past week, crude prices have plunged by more than 20 percent, reversing much of the surge that came after Russia’s invasion of Ukraine. Tens of millions residents in provinces and cities including Beijing, Shanghai and Shenzhen are under lockdown amid an outbreak of the Omicron variant of the coronavirus.

Travel has been cut off between cities, production lines have stopped and malls have been closed. The measures could snarl global supply chains that are still struggling to recover from pandemic disruptions, by slowing down key factory and transportation networks. Companies in China, including Foxconn, the Taiwanese electronics firm that assembles Apple’s iPhones, have suspended operations in the country.

The new measures have hammered the Hang Seng Index in Hong Kong, where many Chinese companies are listed. After it fell 5.7 percent on Tuesday, the index is down 10 percent just this week and at its lowest level since February 2016.

Wall Street had the inverse reaction on Tuesday, with the falling energy costs helping lift share prices. The S&P 500 rose more than 1.5 percent, with gains led by airlines. American Airlines and United were up more than 8 percent on Tuesday, while JetBlue rose more than 7 percent in early trading.

Oil producers tumbled. Chevron and Exxon Mobil both fell more than 6 percent, and Valero Energy was down more than 7 percent, making them among the worst performers in the S&P 500.

Gas prices, which have been steadily rising for weeks amid the conflict in Ukraine, also fell slightly on Tuesday. The average price of a gallon of regular gasoline stood at $4.316, down from a high of $4.325 the day before, according to data from AAA.

Wall Street has been battered this year as threats to the global economy continued to mount. Inflation is climbing at its fastest pace in 40 years, threatening consumer sentiment, and the sudden rise in oil prices in recent weeks has exacerbated the situation. Tuesday’s rally came after a three-day stretch of losses for the S&P 500 that had left the index down more than 12 percent for the year.

The Federal Reserve began a two-day meeting on Tuesday and is expected to announce on Wednesday that it will raise interest rates by a quarter point, as it begins a campaign to cool down the economy.

Investors were also weighing mixed messages about the conflict between Ukraine and Russia as a fourth round of negotiations between the countries’ officials resumed on Tuesday. Mykhailo Podolyak, a Ukrainian representative, said Russia and Ukraine discussed a possible cease-fire and the withdrawal of troops from Ukrainian territory.

“There is so much information investors are taking on board,” said Fiona Cincotta, senior financial markets analyst at Forex.com. Ms. Cincotta said that investors are may be weighing domestic concerns against news from overseas, and deeming the United States a safer place to invest right now.

“With Covid spreading in Asia and the geopolitical tensions in Europe, America seems like the best of a bad bunch right now,” she said.