By Sam Goldfarb and Joe Wallace 

U.S. stocks fell sharply Wednesday, extending their turbulent run as hopes for additional fiscal stimulus dimmed, coronavirus cases rose and investors continued to question the valuations of tech stocks.

Stocks have whipsawed this week: the S&P 500 briefly neared correction territory Monday -- defined as a retreat of 10% from a recent high -- only to rebound Tuesday. One bright spot on both days was the technology sector, which showed signs of stabilizing after dragging down indexes in previous weeks.

But traders were back in selling mode Wednesday, continuing to lighten up on large tech stocks -- such as Apple, Google parent Alphabet and Amazon.com -- that had powered the market higher over much of the summer.

The S&P 500 slid 78.65 points, or 2.4%, to 3236.92, following a rally of more than 1% Tuesday. The Dow Jones Industrial Average fell 525.05 points, or 1.9%, to 26763.13, while the tech-heavy Nasdaq Composite dropped 330.65 points, or 3%, to 10632.99.

Putting pressure on the tech sector, the Justice Department submitted a proposal to Congress to curb longstanding legal protections for internet companies and force them to shoulder more responsibility for managing content on their sites.

Investors were also confronting the risk of a fresh wave of coronavirus in Europe and an uptick in U.S. cases, helping pull down stocks across a range of sectors.

"Markets are really changing very rapidly their mind-set," said Nadège Dufossé, deputy global head of multiasset at Candriam, an asset manager based in Luxembourg.

The Federal Reserve's continued support of the economy should help stocks, but the dwindling chances that lawmakers agree on a new round of economic stimulus before November's election are weighing on sentiment, Ms. Dufossé added.

Reflecting on tech stocks, many investors remain confident that the fallout from the coronavirus pandemic will only accelerate shifts to a more online world that will provide major benefits to the sector. At the same time, worries have increased of late that this year's rally may have stretched valuations to an unsustainable level.

"Some of these names have risen so far so fast, I think that people have to start doing the work and saying, 'Does it make sense for all of these companies to be so strong?'" said Pete Santoro, senior portfolio manager at Columbia Threadneedle.

Recent declines in stocks still pale in comparison to the gains that preceded them. Wednesday marked six months since the S&P 500 reached its low for the year on March 23, over which time the S&P 500 climbed nearly 45%--its best six-month stretch since 2009 when the market was also recovering from a major selloff.

Among individual companies, shares of Tesla fell $43.87, or 10%, to $380.36 after Chief Executive Elon Musk said it could take three years to fully realize large reductions in battery costs, disappointing some investors. Mr. Musk's target to produce 20 million vehicles a year also came without a precise timeline or budget.

Shares of Nike surged $10.24, or 8.8%, to $127.11 after the sportswear company said sales rebounded over the summer. Shares of General Mills gave up early gains to fall 27 cents, or 0.5%, to $57.72 after the Cheerios and Bisquick maker reported stronger sales for its most recent quarter.

Surveys of U.S. purchasing managers indicated manufacturing and service-sector activity kept expanding this month, though at a slightly slower pace than in August.

Meanwhile, surveys of purchasing managers in Germany, France and Japan showed resurgent coronavirus cases were pinching service providers in Europe and Asia. The reports on overseas conditions by data firm IHS Markit suggested a faltering end to the third quarter for the global economy, though the manufacturing sector remained a bright spot. The data suggested output may struggle to return to pre-pandemic levels until a vaccine becomes widely available.

The House passed a short-term spending bill keeping the U.S. government funded through Dec. 11, likely averting a partial shutdown when the funding expires next Thursday.

Still, the focus in Congress has shifted this week to the efforts to fill the late-Justice Ruth Bader Ginsburg's seat in the Supreme Court, rather than reaching an agreement over a second coronavirus-relief package, investors said.

Testifying before a congressional panel, Fed Chairman Jerome Powell repeated his view that more government spending would allow the Fed to more quickly meet its goals of a healthy labor market and 2% annual inflation.

U.S. government bonds remained in a narrow range. The yield on 10-year Treasury notes edged up to 0.676% from 0.663% Tuesday. The WSJ Dollar Index gained 0.6%, climbing for a fourth day.

U.S. crude-oil for November delivery gained 0.3% to $39.93 a barrel, while gold for September delivery lost 2% to $1859.90

Overseas markets were mixed. The Stoxx Europe 600 rose 0.6%, while China's Shanghai Composite Index edged up 0.2% and Japan's Nikkei 225 closed slightly lower.

Write to Sam Goldfarb at sam.goldfarb@wsj.com and Joe Wallace at Joe.Wallace@wsj.com

(END) Dow Jones Newswires

September 23, 2020 16:53 ET (20:53 GMT)

Copyright (c) 2020 Dow Jones & Company, Inc.