NEW YORK (CNNMoney) -- Stocks plunged Thursday in their single worst day since the 2008 financial crisis.
The Dow tumbled 512 points -- its ninth deepest point drop ever -- as fear about the global economy spooked investors.
"The conventional wisdom on Wall Street was that the economy was growing -- that the worst was behind us," said Peter Schiff, president of Euro Pacific Capital. "Now what people are realizing is the stimulus didn't work, and we may be headed back to recession."
U.S. markets were already sharply lower on widespread worries, including the weak job market. But the selling gained momentum as Japanese and European policymakers stepped in with dramatic measures to shore up their financial markets.
There's "total fear" in the market, said Bob Doll, chief equity strategist at the world's largest money manager, BlackRock.
All three major indexes tumbled more than 4% Thursday and erased all their gains for the year. The indexes have also pushed into "correction" territory -- defined as a 10% drop from recent highs. The Dow, Nasdaq and S&P 500 have all fallen 10% in just the last 10 days.
"In the last two weeks, we've been through the ringer," said Rich Ilczyszyn, market strategist with futures broker Lind-Waldock. "When we start looking at the recovery, there's nothing to hang our hats on anymore."