A worldwide selling frenzy on Monday bruised U.S. stocks and sent the Dow Jones Industrial Average plunging nearly 600 points, as investors worried over China’s slowing economy extended a global-market meltdown.

The Dow fell more than 1,000 points within six minutes, its largest single-day slump in history, before staggering back to close down 588 points, or 3.6 percent, its lowest point in 18 months. It marked the second straight day of a 500-point-or-more loss for the Dow, a blue-chip index of 30 large companies.

The Standard & Poor’s 500, a broader look at the market, and the Nasdaq Composite, a tech-heavy index, posted similarly dismal starts before swinging wildly then sinking again to losses of close to 4 percent.

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The global whiplash underscored investors’ shaken confidence in China’s slowing economy and central bank. The world’s second-largest economy is now reeling over what China’s state media is calling “Black Monday,” during which its markets just recorded their biggest one-day nosedive in eight years.

The sell-off and ensuing chaos bruised every industry, wiping out gains in rapid order after a year of mostly steady trading. Some of America’s biggest companies shed tens of billions of dollars in market value in only a few days, and the markets’ early gains have yet to restore those losses.

“This is all about fears of a hard landing in China,” said Campbell Harvey, an economist and business professor at Duke University. The morning’s panicked opening, he added, “is bare-faced evidence of a market overreaction.”

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The trading roller-coaster roiled the world’s most valuable company, Apple, which began the morning down 13 percent before bouncing back into positive territory — and then sagging back nearly 2 percent into the red. The $592 billion tech giant lost more than $58 billion in market value last week.

The dismal opening marked an unnerving continuation of last week’s free fall. The Dow’s blue-chip index plunged more than 500 points on Friday, capping its worst week since 2011 and entering what Wall Street calls a correction, having tumbled 10 percent from its May peak.

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S&P 500 companies lost more than $1 trillion in market value last week, and the Dow and other indices are on track to record their dreariest month since February 2009.

The panicked opening and steep downfall had a “flash crash-type feel to it,” Credit Suisse analysts wrote Monday, with some making comparisons to the “Black Monday” trading disaster of 1987, when the Dow plummeted more than 22 percent.

Early Monday, the S&P 500 came startlingly close to a tripping point in which trading would have been shut down for 15 minutes to help halt the disarray.

Though the recent investor rally has helped, the Dow is still down 11 percent from the start of the year.

On Friday, a key barometer of Chinese manufacturing sagged to its lowest point since the global financial crisis, following shortly after Beijing earlier this month surprised investors with a move that helped devalue the nation’s currency.

China’s benchmark Shanghai Composite index has fallen by nearly 40 percent since June, after soaring more than 140 percent last year. Markets in Europe also plummeted, and Asian shares on Monday hit a three-year low.

“There’s no doubt the Chinese economy is slowing,” said Jim Dunigan, chief investment officer at PNC Wealth Management. “But the question now is: How much is it slowing, and what will the government step up to do about it?”

[World markets lose ground amid ‘Black Monday’ for Shanghai index]

China’s woes stoked fears over commodities and forced oil prices further down. Brent crude oil, the global benchmark, dropped to about $43.50 a barrel, sinking below the $45 mark for the first time since 2009. U.S. light crude fell 4 percent, to $38.90 a barrel, a six-year low.

Demand for U.S. Treasury bonds also heated up as investors flocked to safety. Yields for the 10-year bonds dwindled below 2 percent for the first time since April.

The markets’ mayhem could further dent workers’ 401(k) retirement accounts and could affect the Federal Reserve’s plans to raise interest rates for the first time in a decade.

The weakness overseas comes at a time when the U.S. economy is relatively strong, fueled by encouraging signs in the job market and better-than-expected corporate results.

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President Obama was briefed on the turmoil, White House press secretary Josh Earnest said Monday. He added that the Treasury Department “has been closely monitoring” markets in China and across the world.

Earnest used the volatile markets to call on Congress to avoid a government shutdown, pass spending bills and reauthorize the Export-Import Bank, saying, “The administration, certainly the president, is very mindful of how this would be a particularly bad time for a self-inflicted wound.”