U.S. stocks fell sharply Thursday, extending a week of wild swings as jittery investors continued to fret over the potential economic fallout from the coronavirus outbreak.

The growing understanding that the spread of infections — and the resulting damage to the economy — may not slow anytime soon is pulling sharply on markets. That pull has taken turns this week with the increasingly worldwide push that governments and central banks are trying to give markets through spending plans and interest-rate cuts.

Treasury yields fell to more record lows as the market swung back to fear about the effects of a fast-spreading virus in its latest yo-yo move. Now that a growing list of companies are warning about how the virus is hitting their sales and profits, investors are left with a lot of uncertainty about just how much economic growth and corporate profits will be affected.

“Until the coronavirus started spreading in our communities recently, the stock market had held up well and was trending higher,” says Nick Giacoumakis, president and founder at New England Investment & Retirement Group. “Now that we’re seeing outbreaks in Washington and California, it’s become a much bigger issue for investors since this could disrupt supply chains and earnings growth even further for companies.”

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Charlie Smith, chief investment officer at Fort Pitt Capital Group, agrees.

"Has the reaction to the virus and the potential economic problems that we create through a response of fear greater than the problems generated by the virus itself?" Smith says. "We still don't have the answer yet."

The Dow Jones Industrial Average dropped 969.58 points to close at 26,121.28 Thursday, erasing the majority of Wednesday's gains. Just a day earlier, the blue-chip average soared nearly 1,200 points, in part on hopes that more aggressive moves by governments and central banks around the world could help contain the economic fallout.

The Standard & Poor’s 500 slumped 3.4% to finish at 3,023.94, with the broad index moving more than 2% for a fourth consecutive day for the first time since the summer of 2011. The technology-heavy Nasdaq Composite slid 3.1% to end at 8,738.59.

With Thursday's losses, the S&P 500 index slid deeper into a correction, or drop of 10% from a recent high, sliding about 11% from its Feb. 19 record.

Get used to such vicious swings, which will likely keep going as long as the number of new infections continues to accelerate, many analysts and professional investors say.

"We expect markets to remain volatile,” Mark Haefele, chief investment officer at UBS Global Wealth Management, said in a note. “The unfolding nature of the coronavirus threat—both real and perceived—is not yet quantifiable, and, as such, the current global policy response can't immediately be judged as sufficient or insufficient for restoring investor confidence in the short term."

Factories in China are gradually reopening, and a return to a sense of normal life may even be on the horizon following swift and severe actions by the government to corral the virus.

But elsewhere in the world, the mood is much darker. In the U.S., the death toll climbed to 11 due to the virus. California declared a statewide emergency late Wednesday, joining Washington, Florida and Hawaii. Southwest Airlines warned its investors that it’s seen a significant decline in demand in recent days and an increase in customers cancelling trips.

Bond investors continued to pile into safe-haven assets such as U.S. government bonds. The yield on the 10-year Treasury fell to 0.92% Thursday, from 0.99% late Wednesday. It earlier threatened to drop below 0.90% for the first time in history.

On Friday, investors will sort through the monthly jobs report to see whether the U.S. labor market remained strong in February.

Contributing: The Associated Press.