Alcoa, the aluminum producer, beat Wall Street earnings estimates on Tuesday night but said it expects a slowdown in China to weaken demand for aluminum. The company's stock fell 43 cents Wednesday to $8.69.
Alcoa is often used as a weather vane of global economic growth. "And judging by Alcoa's massive inventory of aluminum, it seems pretty anemic," said Jack Ablin, chief investment officer at Harris Private Bank in Chicago.
Chevron, the country's second-largest oil company, warned late Tuesday that slumping oil prices and production would cause earnings to be "substantially lower." It blamed Hurricane Isaac for disrupting production at a Mississippi refinery.
On Tuesday, the Supreme Court also refused to block a $19 billion judgment levied against Chevron by an Ecuadorian court for pollution in the Amazon. Chevron's stock sank $4.22 to $113.12.
The Dow sank 102 points to 13,371 shortly after 1 p.m. Alcoa was the biggest loser among the 30 stocks that make up the average. The Standard & Poor's 500 index fell nine points to 1,432.
A loss for the Dow would be its third in a row. A loss for the S&P, which measures the broader market, would be its fourth.
Stocks in the energy and materials industries, whose fortunes hinge on economic growth, slumped the most. Consumer staples were the only industry group to rise, thanks to Wal-Mart Stores and Costco.
Wal-Mart surged $2.51 to $76.64. The president of its U.S. division told Wall Street analysts that the retail giant plans to open more small-scale stores, including its Express chain, to compete with discount retailers and drugstore chains.
Costco posted stronger sales and earnings than forecast as more people signed up to buy the company's diapers and groceries in bulk. Costco's stock gained $3.20 to $102.84.
In other trading, the Nasdaq lost 17 points to 3,048. The yield on the benchmark 10-year Treasury slipped to 1.70 percent, down from 1.71 percent late Tuesday.
The S&P 500 is now down 2 percent for the week. The Nasdaq has lost nearly 3 percent.
Alcoa's earnings report marks the unofficial start to the quarterly earnings parade, and this earnings season is expected to be the weakest in three years. Analysts project that companies in the S&P 500 will say third-quarter earnings shrank 1 percent compared with the same quarter of last year.
Ablin said investors need a solid reason to buy stocks, given their strong performance this year. "My sense is that, with these downbeat earnings announcements, there's not much around right now."
Among other companies making big moves Wednesday:
— Yum Brands jumped 8 percent, the top stock in the S&P 500 index. The parent of Taco Bell, Pizza Hut and other fast-food chains said results from China stores should remain strong, even as the Chinese economy slows. Yum gained $5.32 to $71.03.
— FedEx gained 4 percent. The world's second-biggest package delivery company unveiled a restructuring plan Monday aimed at raising profits by $1.7 billion within three years. FedEx promised to shed jobs and underused aircraft. FedEx rose $3.77 to $89.35.
— Toyota Motor Corp. sank 1.5 percent after the carmaker recalled a total of 7.4 million vehicles worldwide for a for a faulty power-window switch, the latest in a series of recalls for Toyota. The recall announced Wednesday affects more than a dozen models produced from 2005 through 2010. Toyota's stock dropped $1.49 to $74.57.