Hundreds of people in China's southern Guangdong province protested the expansion of a coal-fired power plant on Sunday, state media reported, the latest sign of public discontent over pollution.

Residents had complained of smog in Heyuan city since the power plant there began operations in 2008, and officials recently approved a second phase for the project, the official Xinhua news agency reported.

"There has been a strong police presence, though no reports of violence since the protest began at around 10 a.m.," Xinhua said. Residents had collected more than 10,000 signatures in March on a petition opposing the plant's expansion, it added.