In some neighborhoods in the southeast, prices have dropped by 10 to 40 percent.

In other parts of the country, transactions have fallen, but prices have only started to follow. For instance, the number of home sales has plunged by two-thirds in Harbin in the northeast, though prices are down as little as 4 percent from the same period last year.

“People are thinking more carefully and taking much longer before they decide to buy or not to buy property,” said Hwang Sha, a real estate broker in Xiamen in east-central China.

Cities deep in China’s interior are least affected. Dan Yian, a real estate agent in Chongqing, the largest city in southwestern China, said that the volume of housing transactions there had slowed by 20 to 30 percent so far this year. But prices have not yet fallen from a stable level of $730 a square meter, or 10.76 square feet, which works out to nearly $66,000 for a typical apartment of about 970 square feet.

Export-dependent coastal cities in mainland China have had the steepest downturns in their real estate markets. Some of those problems are starting to make ripples elsewhere in Asia.

Freddy Wu, the chief executive of Hong Kong Property Services, said his real estate agency had seen mainland investors default in recent months on a tenth of their purchases of Hong Kong apartments, forfeiting the down payments that they made.

“A lot of investors from China have their cash tied up in the mainland stock market and in mainland real estate, so they would rather take a loss now,” instead of being forced to sell mainland investments at a loss to come up with the cash to complete purchases in Hong Kong, Mr. Wu said.