SHANGHAI -- Tony Yu grew rich helping build China into the world's factory floor.

Over a decade, his small firm outfitted more than a thousand assembly lines with specialized equipment: pumps and pipes to sluice chemicals through high-tech plants. Business was so good his biggest challenge was keeping up with manufacturers impatient to cut the ribbons on their next plant. Mr. Yu poached engineers from rivals as he grew and acquired a mansion overlooking Shanghai's fanciest golf course.

Now his order book is emptying. China's February exports fell nearly 26% from a year before, the fourth in a series of worsening monthly declines. The building boom in Chinese factories is over, and Mr. Yu is casting about for business ideas. "We have ridden the wave of economic development in the last few years," he says. "We are at a loss as to what to do in the immediate future."

His fate echoes a broader challenge for China itself. The country has relied heavily for its often double-digit growth on a furious pace of investment in manufacturing. More than 40% of China's gross domestic product traces to factory construction and other kinds of fixed-asset investment.

Contributing to this have been hundreds of thousands of bootstrap entrepreneurs like Mr. Yu who appeared from nowhere, helping the Chinese economy to multiply 14-fold, adjusted for inflation, since 1980. Their bold dives into business -- dubbed xia hai, or "jump into the sea" -- and often unorthodox methods both thrilled and chilled the wider business community. Tiny firms shocked global goliaths with aggressive cost-cutting and sometimes corner-cutting as well.