Stocks plunged in the final hour of trading today, sending the Dow Jones industrial average down more than 675 points -- to its lowest level in five years.

The decline happened after a major credit ratings agency said it was considering cutting its rating on General Motors Corp., one of the 30 companies that makes up the Dow Jones Industrials.

The Standard & Poor's 500 index also fell more than 7 percent today.

The declines came on the anniversary of the closing highs of the Dow and the S&P. The Dow has lost 5,585 points, or 39 percent, since closing at 14,198 a year ago. The S&P 500, meanwhile, is off 42 percent in that period.

Today's selloff came as Standard & Poor's Ratings Services put GM and its finance affiliate GMAC under review to see if its rating should be cut. GM has been struggling with weak car and truck sales in North America.

The stock market has dropped for seven consecutive days -- part of a crisis of confidence in the nation's financial industry.

That crisis has created a shaky forecast for Louisiana's economy, despite the state's flush treasury in the wake of high oil prices and continued rebuilding from Hurricane Katrina, a leading economist said today.

LSU economics professor Loren Scott predicted job growth in Louisiana will virtually stop next year due to the nation's recession. He said it should pick up in 2010.

Billions of dollars in construction involving industrial expansions, levee and highway projects, rebuilding from the hurricane and less exposure to the nation's credit crisis will help Louisiana fare better than other states, Scott said.

ABC News contributed to this report