Twenty-one people who police say violated the law during a protest on Sunday against the planned construction of a garbage incineration plant in Zhaoqing, Guangdong province, have been taken away for questioning.

"The lawbreakers threw stones and bottles of mineral water at police and other law enforcement personnel during the protest in Lubu township in Zhaoqing's Gaoyao district," said Duan Jianxin, an official in the city's publicity department. "Some police officers were injured."

Police urged those who violated the law during the protest to give themselves up, he said.