HONG KONG — After almost two decades of nearly unceasing increases in real estate prices and construction across China, one of the world’s longest-running bull markets finally seems to be stalling, with broad consequences for the country’s economy and possibly its politics.

Prices are falling for both new and old apartments. The volume of deals is drying up. And developers are pulling back, furloughing workers and delaying new projects. In the latest sign, housing starts plummeted 25 percent in April from a year ago, the Chinese government announced on Tuesday.

It is a severe blow for a country where real estate sales offices have become ubiquitous and tower cranes are jokingly described as the national bird.

Su Hua, a real estate broker in Shenzhen, had his highest commissions ever last year, as a speculative frenzy prompted families all over China to buy and sell apartments at a brisk pace. But he sat in a deserted office late last week with several silent phones on his desk. His income has halved so far this year.