“Basically half the factory was shut down and one dormitory was empty,” Ms. Gallagher said.

In interviews, factory executives across the country complained of being forced to give double-digit raises in order to find and keep young workers at all skill levels. Three or four years ago, said Zhong Yi, vice general manager of a leather-jacket manufacturer in Hangzhou in east-central China, 800 to 1,100 yuan a month ($105 to $145) “was a good salary.”

“Now,” he said, “1,500 is the bottom” ($198).

Chinese officials are quick to say that there is no overall shortage of labor — rather, there is a shortage of young workers willing to accept the low wages that prevailed in the 1990s. Factories in cities like Guangzhou advertise heavily for young workers, even while employment offices consider it a success if someone over 40 can find any

Plant owners’ refusal to hire blue-collar workers over 35 or 40 is colliding with the demographic reality of China’s one-child policy. The number of workers in the 20-to-24-year-old range is already shrinking as more of them go to universities instead of entering the work force after high school, and the International Labor Organization projects that workers in this age range will edge slowly downward through at least 2020.