Stocks took a stomach-turning dive on Monday, sending the Dow Jones industrial average down more than 1,000 points in a matter of seconds. The market recovered some of its losses but was still way down for the day.
The sudden plunge was reminiscent of the fear that gripped the markets during the financial crisis of 2008, and it followed big declines in Asia and Europe.
UPDATE 8/25: Dow Makes Gains After a Day of Turbulence
Investors around the world are worried about China, the world's second-largest economic power and a huge market for American products. China devalued its currency two weeks ago and has shown other signs of economic weakness.
Two hours into trading, the Dow was down 454 points, or 2.8 percent, at 16,005. At its worst point, just after the opening bell, the Dow was down an eye-popping 1,089 points, or 6.6 percent.
"Fear has taken over," Adam Sarhan, CEO of the investment company Sarhan Capital, told CNBC. "The market topped out last week."
Last week was the worst for the market in four years, and the Dow had already entered what is known as a correction, down more than 10 percent from its all-time high, reached in May.
On Monday, the Standard & Poor's 500 index, a broader gauge of the overall market, was down more than 5 percent before recovering, and the Nasdaq, loaded with technology stocks, was down more than 8 percent.
In percentage terms, the drop in the Dow, even at its worst point on Monday, was not nearly as severe as in historic stock market crashes. In 1987, on what came to be known as Black Monday, the Dow fell by 22 percent.
But the free-fall was more than enough to get investors' attention. It also got the attention of Lawrence Summers, the former treasury secretary.
Few stocks were immune as the free-fall extended to the biggest names in American commerce. General Electric fell 11 percent, Verizon 12 percent and Apple 11 percent. All recovered their losses significantly.
The sell-off on Monday swept west across the globe. Stocks closed down more than 8 percent in Shanghai and more than 4 percent in Tokyo. Markets in London, Paris and Frankfurt were all down more than 4 percent.
"It is going to be a bad day," CNBC's Jim Cramer said on TODAY. "It's probably going to be a bad week."
There was no immediate reaction from the White House, but the jolt to the market shook the presidential campaign.
The worldwide market decline has extended to commodities, including crude oil, which is below $40 per barrel for the first time since the financial crisis six years ago.
That is good news for drivers — the national average for gasoline is $2.59 a gallon, down 14 cents in a month — but bad news for energy stocks, which make up a significant chunk of Americans' retirement portfolios, and state economies that depend on oil.
Traders have been putting their money in investments they consider safer, including government bonds and gold.
The market's last correction was in April 2011. Cramer pointed out that the American economy is much healthier than it was then. Unemployment in April 2011 was 9.1 percent, compared with 5.3 percent today.
He also cautioned that some of the factors that could send the U.S. market far lower are unlikely — a big rise in unemployment, a spike in interest rates or inflation, or a banking crisis.
For now, though, "There is just a tremendous decline coming from China," he said, "and we are importing it."