NEW YORK - A runaway train of a sell-off turned the anniversary of the stock market peak into one of the worst days in Wall Street history Thursday, driving the Dow Jones industrials down a breathtaking 679 points and deepening a financial crisis that has defied all efforts to stop it.

Stocks lost more than 7 percent, $872 billion of investments evaporated, and the Dow fell to 8579. When the average crashed through the 9000 level for the first time in five years in the final hour of trading, sellers had only begun to hit the gas pedal.

As bad as the day was, even worse was the cumulative effect of a historic run of declines: The Dow suffered a triple-digit loss for the sixth day in a row, a first, and the average dropped for the seventh day in a row, a losing streak not seen since 2002.

"Right now the market is just panicked," said David Wyss, chief economist at Standard & Poor's in New York. "Nobody wants to take on any risk. Everybody just wants to get their money and put it under the mattress."

It all took place one year to the day after the Dow closed at its record high of 14,164. Since that day, frozen credit, record foreclosures, cascading job losses and outright fear have seized the market and sapped 39 percent of its value.

Paper losses for the year add up to an staggering $8.3 trillion, according to preliminary figures measured by the Dow Jones Wilshire 5000 Composite Index, which tracks 5,000 U.S.-based companies representing almost all stocks traded in America.

It was the second straight day that Wall Street was rocked by a final-hour sell-off, but this one was particularly shocking.

Most of the day was relatively calm, and the trading floor was quieter than usual because of the Jewish holiday of Yom Kippur. Wall Street awoke to news the federal government was brandishing a new weapon against the financial crisis - considering seeking an equity stake in major U.S. banks in order to stabilize them.

But that step appeared to be as ineffectual as the others Washington has rolled out in recent weeks, including a $700 billion bailout of the financial industry, a coordinated interest rate cut by central banks around the world and direct lending by the Federal Reserve to private companies to provide them with short-term cash.

Acquiring a stake in the banks would be yet another startling intervention by the government in the free market, but economists said President Bush was left with little choice because of the credit markets, where tight lending has choked off the everyday cash that is the lifeblood of the economy.