Fears are growing that the global downturn could be far more punishing and long lasting than initially feared — potentially enduring into next year, and even beyond — as governments intensify restrictions on business to halt the spread of the pandemic, and fear of the virus impedes consumer-led economic growth.

“The market is sort of steeling itself for the onslaught of bad news over the next couple weeks,” said Julian Emanuel, chief equity and derivatives strategist at the brokerage firm BTIG.

On Thursday, the U.S. government will report how many people filed for unemployment last week, and the data could show that as many as 5 million workers lost their jobs as people stay home and factories shut down.

“There was an expectation that April 30 was perhaps a doable date in terms of reopening the economy,” said Mr. Emanuel. “I think the market is trading today as if that date is more like the end of May.”

On Wednesday, the decline was led by companies that have become familiar targets of investor unease during the crisis. Airlines were the worst performing sector in the S&P 500 as government data showed a staggering drop in passenger traffic through airports. United Airlines fell 19 percent, and American Airlines dropped 12 percent.

Cruise operator Carnival was the worst performing stock in the S&P 500, with a decline of 33 percent, while rival Royal Caribbean fell 20 percent.