Sales of new homes tumbled in June by the largest amount in five months, provoking new worries on Wall Street about how much the prolonged housing slump will hurt the overall economy.

The Commerce Department reported Thursday that sales of new single-family homes dropped by 6.6 percent last month to a seasonally adjusted annual rate of 834,000 units. The decline was more than triple what had been expected and was the largest percentage drop since sales fell by 12.7 percent in January.

The fall in new home sales was the latest piece of evidence this week of housing's troubles. Sales in the much larger existing home market also fell in June, dropping by 3.8 percent to an annual rate of 5.75 million units, the slowest pace in nearly five years. Also this week, Countrywide Financial, one of the largest mortgage lenders, reported a sharp drop in second-quarter profits.