SHENYANG, China — Not long past the break of dawn, after downing a bowl of hot porridge and dropping off his son at school, Zhang Yuzeng made his way to a street corner near the Nanyun River. There, under the poplar trees, he rummaged through his toolbox.

Pliers, check. Club hammer, check. Cigarettes, check.

Mr. Zhang hung a sign on his scooter — “Electrician, carpenter, plumber” — and pumped a techno mix through his headphones. Then he waited.

“There is no other way,” he said. “If you don’t show up, you won’t be able to make a penny.”

Nearly every morning for the last two years, Mr. Zhang, 42, has advertised his skills and looked for work here at the Lu Yuan labor market in Shenyang, one of northeast China’s largest cities. Not so long ago, his prospects were decent: A day of painting walls or fixing toilets could fetch $50 or more.