Price of crude oil slumps, dragging down energy companies and the rest of the stock market

Another plunge in the price of oil is driving stocks sharply lower in afternoon trading.

Energy stocks slumped as the price of crude briefly dipped below $50 a barrel.

The Dow was down 295 points, or 1.7 percent, to 17,539 as of 12:43 a.m. Eastern time. It was down as much as 315 earlier.

The Standard & Poor's 500 index fell 33 points, or 1.6 percent, to 2,024. The Nasdaq composite fell 56 points, or 1.2 percent, to 4,671.

Energy companies had the worst declines in the S&P 500 index. Denbury Resources and Noble Energy each lost 9 percent.

The euro sank to a nine-year low as traders worried about whether Greece will stay in Europe's currency union.