Several hundred people gathered in Jiangmen's city centre on Friday morning to protest against a planned uranium processing plant in the Guangdong city.
“Jiangmen doesn't want radiation", one banner carried by demonstrators said. "We want children, not atoms," said another.
Police appear to have been anticipating the protest with Jiangmen city government building being cordoned-off.
One group of protesters gathered in front of the building, another group meet at the Donghu Lake park.
Two protesters, who declined to be identified, said that the protest had been organized via QQ and WeChat, two social messaging services, at least two days ahead of the protest.
One local said that the local government had held an emergency meeting last night to prepare for the protest. According to one demonstrator, the public protest lasted from 8am to 11:30am and is planned resume in the afternoon.
Some protesters were holding banners calling for another protest on Sunday.
Thee 30-hectare plant would carry out uranium conversion, enrichment and fuel fabrication, the Jiangmen City Development and Reform Bureau said in an earlier statement.
The plant's construction some 100km from Hong Kong and Macau has sparked health concerns in both cities as well.
The Heshan government under the administration of Jiangmen held a press conference earlier on Friday morning defending the project. Heshan mayor Wu Yuxiong said that the local government has decided to extend the period in which the risk assessment report is publicly accessible by a further ten days.
Microblogs about the protests have been quickly censored, indicating increased sensitivity about a backlash. Earlier this year, two demonstrations against a gas refinery in Kunming have caused a public backlash. A similar protest in Chengdu had been repressed.
Photos from earlier on Friday: