DONGGUAN, China — Thousands of foreign businesspeople, primarily Taiwanese, helped turn this southern Chinese city into one of the world's busiest export manufacturing centers.

　　Now, amid rising wage and pension costs, energy shortages, tighter government regulation, traffic bottlenecks and other concerns, some of them are starting to look elsewhere. Their restlessness reflects a dark side to China's economic boom, as growth pains and other issues prompt companies to reconsider starting up or expanding in China.