BEIJING (Reuters) - Police in southern China have detained 21 people involved in a protest against a planned garbage incinerator, the latest incident of environment-related unrest in the country.

In a statement late on Sunday, the government of Gaoyao district in Guangdong province’s Zhaoqing city said about 1,300 people had gathered to protest earlier in the day, which had caused traffic problems.

While the protesters were dispersed by the early afternoon and there was no “drastic behaviour”, 21 people have been taken in for questioning, it added.

Zhaoqing police said on their official microblog that the situation had now returned to normal.

However the official China Daily said there had been some violence.

“The lawbreakers threw stones and bottles of mineral water at police,” propaganda official Duan Jianxin told the newspaper. “Some police officers were injured.”

The China Daily said some residents were worried the garbage incinerator could pollute the environment, but that the government has denied this would happen.

Tens of thousands of “mass incidents” - the usual euphemism for protests - happen in China each year, spurred by grievances over issues such as corruption, pollution and illegal land grabs, unnerving the stability-obsessed ruling Communist Party.

Last month thousands of people protested against a waste incineration project in central China, also over fears it would damage the environment and residents’ health.