U.S. stocks fell at the opening of trading Thursday on more signs of economic weakness around the world.

The Dow Jones industrial average dropped 500 points by mid-morning.

Investors are responding to new economic numbers showing sluggish results.

The latest report revealed 408,000 people applied for unemployment benefits last week -- an increase from 399,000 the week before and the most in four weeks.

Consumers were under even more pressure at the cash register last month as inflation rose 0.5 percent in July, the highest since March.

Existing home purchases also dropped in July for the third time in four months.

Stocks in industries that depend on a growing economy fell the most, Thursday.

Industrial stocks in the Standard & Poor's 500 fell 5.4 percent, technology stocks 5.1 percent and financial stocks 4.6 percent.