Commodities also slumped as worries about a global recession and rising stockpiles of some raw materials pulled crude oil, gold and grains prices lower.
Shares on Wall Street hit a one-month low, with the S&P 500 index down nearly 2 percent as it dropped below the 1,200-point level for the first time since October.
The tech-heavy Nasdaq index was also down almost 2 percent, as was Dow Jones industrial average , following through on last week’s declines as a congressional “super committee” was expected to concede defeat in its bid to lower the US deficit.
“These days it’s pretty hard to have confidence in the political side of things ” said Rick Bensignor, chief market strategist at Merlin Securities in New York.
Gold futures lost nearly 3 percent, trading at around $1,675 an ounce. The precious metal, with record highs above $1,900 just in September, is on course to finish the year down 17 percent.
US oil prices moved between $95 and $97 barrel in volatile trading.
Investors took refuge in safe havens, pushing yields on benchmark 10-year US bonds down to 1.96 percent from 2.01 percent on Friday.
The dollar hit a six-week high versus a currency basket but then pared some of its gains after data showed US existing home sales unexpectedly rose in October as low mortgage interest rates and rising rents led more homebuyers into the market.
Light trading volume, expected throughout the week due to Thursday’s US Thanksgiving holiday, could add to market volatility, traders said.
“If you just don’t have enough buyers stepping in then it doesn’t take a lot of sellers to make market move down,” noted Bensignor.
Around 2:45 p.m. EST (1945 GMT), the Dow was down 246.20 points, or 2.09 percent, at 11,549.96. The Standard & Poor’s 500 Index fell 21.36 points, or 1.76 percent, to 1,194.29. The Nasdaq Composite Index was down 47.25 points, or 1.84 percent, at 2,525.25.
A takeover deal provided a bright spot as Pharmasset Inc. surged 85 percent to above $134 after Gilead Sciences Inc. agreed to buy the company for $11 billion in cash. Gilead tumbled 10 percent to around $35.
In Europe, stocks hit 6-week lows as Moody’s warned about France’s rating outlook and Spanish yields rose following election of a new government.
World stocks as measured by MSCI were down 2.3 percent for a 12 percent year-to-date loss. More volatile emerging market stocks lost 2.6 percent.
In Europe — the heart of the debt storm — the FTSEurofirst 300 index finished down 3.3 percent, putting it more than 17 percent lower for the year.
