By Nathaniel Popper | Wall Street fell off a cliff Thursday, with the Dow Jones industrial
average dropping nearly 1,000 points, before recovering to close down
347 points on the day.

With less than 90 minutes left in the trading day, the Dow was down more
than 250 points points on continued concerns about Greece’s debt crisis
and the possibility it could set off another global financial meltdown.
Then, in about 15 minutes, the blue-chip average plummeted about 700
more points, then promptly regained that amount.

Traders and regulators scrambled to explain the sudden drop. One rumor said a trader accidentally typed in an order to sell billions of Procter & Gamble shares, rather than millions.

“There were a number of erroneous trades,” said Rich Adamonis, a spokesman for the New York Stock Exchange.

Thursday was the third straight day that the Greek debt crisis hit U.S. stocks. Televised images of violent protests in Athens unnerved already anxious investors, traders said.

“This has been building and building and building — today is the straw that broke the camel’s back,” said Alan Ruskin, the chief international strategist at RBS Greenwich Capital. “I’m not sure what the straw was, but it was only going to take a straw.”

The Dow ended down 347.80 points, or 3.2%, at 10,520.32. The Standard & Poor’s 500 index also fell 3.2%.