HONG KONG — The police in southern China have arrested at least three workers’ rights leaders in recent days, labor groups and activists said on Saturday. The detentions come amid rising labor unrest in southern China, one of the world’s most important manufacturing centers, and are prompting concern that the Communist Party is extending its latest crackdown on civil society to a new arena.

Zeng Feiyang, director of the Panyu Workers’ Center in the city of Guangzhou, was put under criminal detention on Friday on charges of “gathering a crowd to disturb social order,” said the Hong Kong-based nonprofit group China Labor Bulletin and several labor activists. Zhu Xiaomei, a labor organizer, was also detained, as was He Xiaobo, who runs a group in Foshan that helps injured workers.

Mr. Zeng, a lawyer, is one of the most prominent labor organizers in China, and his nongovernmental organization helps workers win management concessions on pay and benefits. Although China, like many Communist countries, restricts the formation of independent labor unions, thousands of workers have nevertheless organized, and often gone on strike.

When the economy in Guangdong, China’s richest and most populous province, was booming, the authorities apparently did not see labor activism as a threat. After strikes by workers at Honda auto parts plants in the province in 2010, for example, many workers won higher wages and benefits.