US stocks tumbled more than three percent across the board on Thursday after fears of contagion from Greece debt crisis triggered unprecedented sell-off during trading.

In early afternoon trading, about 10 minutes to 3:00 PM EDT, the Dow suddenly dropped 998.5 points to below 10,000 points. It was the biggest intra-day point plunge ever, and largest percentage intra-day loss since the market crash on Oct. 19, 1987, when the index closed 22.6 percent lower.

Both Dow and S&P 500 briefly fell into negative area for the year, while Nasdaq down more than nine percent early in the session.

Dow experienced a 1,010.14-point-swing, the second biggest intra-day point-swing ever, as it went down about 700 points in 15 minutes and rebounded about 600 points in 20 minutes.

The New York Stock Exchange said there were no system errors during the Dow's plunge as speculation of bad trades swirled through the market. But the NYSE spokesman Rich Adamonis said " there were a number of erroneous trades" during the plunge. The Nasdaq OMX Group Inc. said it is working with other markets to review the plunge.

But the market had been heading downward as fears of the spreading of Greece's sovereign debt crisis mounted. The plunge came shortly after the approval of a set of new austere measures in the Greek parliament sparked social riot in Athens.

The euro extended its decline against the US dollar to a fresh 14-month low, putting commodities under great pressure. Crude oil prices tumbled to US$77.11 a barrel on Thursday, more than 10 percent down from loss compared with Monday 's close and the lowest level since February. Investors were also worried a spiking dollar could cut into earnings of US companies as Europe was a major market for lots of them.

Thursday's economic data provide little boost for the market. According to the Labor Department, initial claims for unemployment insurance fell by 7,000 to a seasonally adjusted 444,000. It was the third straight time for the number to drop, a sign the job market is slowly improving but the decline was smaller than economists had expected.

As of market closing, the Dow Jones industrial average dropped 347.80, or 3.20 percent, to 10,520.32. The Standard & Poor's 500 index tumbled 37.72, or 3.24 percent, to 1,128.15 and the Nasdaq lost 82.65, or 3.44 percent, to 2,319.64.

(Xinhua News Agency May 7, 2010)