GUANGZHOU -- Police in south China's metropolis of Guangzhou, capital of Guangdong Province, have detained 18 people who allegedly committed violent acts while staging protests on Sunday, local police said Wednesday.

The suspects were allegedly involved in several violent incidents, including smashing a Japanese-brand car, shop windows and billboards, although most people behaved rationally during the protests, according to the press office of the Guangzhou Public Security Bureau.

Local police initially announced on Monday via Sina Weibo, a popular microblogging site, that 11 suspects had been detained.

Police are investigating the acts of violence and have called on the public to provide clues and evidence.

Police in east China's port city of Qingdao also announced Wednesday that six people have been detained for alleged violent acts committed during anti-Japan protests that occurred last Saturday.

A man surnamed Qi allegedly broke into a Japanese store, smashed several counters and stole digital cameras and sneakers, the police said.

Another five suspects allegedly attacked auto shops and smashed or set fire to Japanese cars, according to the police.