Stocks Get Slammed; Dow Drops Nearly 400 Points

The Dow and S&P 500 have lost more than 10 percent from their May highs.

Stocks plunged at the open and the sell-off continued all day. The Dow and S&P 500 are down more than 10 percent from their May highs, pushing them into "correction territory."

All 30 stocks in the Dow lost ground. January is now the Dow's worst month since February 2009.

The Nasdaq has not experienced these deep losses since 2008. The S&P 500 broke below its Aug. 24 low to trade at its lowest level since October 2004.

The rout in oil prices and concerns over China’s slowing economy fueled the sell-off. U.S. crude prices fell below $30 a barrel and are now trading at 12-year lows.

New oil supplies from Iran, which is starting to ramp up production after an easing of international sanctions, also put downward pressure on oil prices.