BEIJING - Local authorities across China have vowed to investigate and punish violent demonstrators involved in the anti-Japan protests throughout the country over the weekend.

Masses of protestors took to the streets to vent their sentiments in many Chinese cities, after Japan's announcement to "purchase" the Diaoyu Islands. While most of the activities remained peaceful, some participants resorted to violence, smashing Japanese-brand cars, looting Japanese stores and restaurants, as well as burning Japanese-invested factories.

While deploying a heavy police presence to maintain order at the protest sites, local authorities have called for rational patriotism and pledged to get tough with the illegal "smashing and looting" acts.

Police in Guangzhou, capital city of southern Guangdong province, said Monday they had detained seven people who damaged a Japanese-brand sedan, three who smashed store windows and another who destroyed two billboards during protests on Sunday.

On Sunday, some protestors barged into the five-star Garden Hotel Guangzhou that houses the Japanese consulate and a Japanese restaurant. The hotel lobby and the restaurant were damaged.

Violence was also reported in Qingdao, eastern Shandong province, and Xi'an, capital city of northwestern Shaanxi province.

Angry demonstrators burned two Japanese companies and set four 4S stores of Japanese-brand cars on fire Saturday in Qingdao's Huangdao District. A Japanese chain store in the area was also damaged.

The city's public security bureau said Monday via its official account on Sina Weibo, China's most popular microblogging service, that they had caught several people suspected of being involved in the protests.

The city government has beefed up security in the Japanese consulate, Japanese-funded stores and other Japan-related institutions. It has also rolled out measures to ensure the safety of 805 Japanese companies and 3,500 Japanese nationals living in Qingdao.

The public security bureau of Xi'an said it has adopted effective and resolute measures to crack down on those who have committed illegal acts during the protests on Saturday.

The flare-up in Xi'an has been brought under the spotlight as microblogger "Ranxiaoqi777" said on Sina Weibo that her uncle was beaten by a protestor at around 3:30 p.m. Saturday in the city.

A photograph uploaded by "Ranxiaoqi 777" showed a man lying with his head bleeding in front of a white Japanese-brand sedan. The post has been forwarded by more than 90,000 times and followed by over 16,000 comments, with many criticizing the beating.

To prevent future turmoil, Xi'an police have issued an order, forbidding any forms of unapproved protests and instigating such activities through mobile phone and Internet messages.

"Anyone should act in line with laws while showing patriotism. We will not tolerate the illegal acts of smashing and looting and other behaviors jeopardizing citizens' legitimate rights, which were committed in the name of 'safeguarding the country's interest,'" said the statement.

Police in Changsha, capital city of central Hunan province, have made similar pledges as a large Japanese-invested department store was looted on Saturday with luxurious wristwatches and cosmetics stolen.

In addition, police in Xi'an, Changsha and Guangzhou encouraged citizens to offer tip-offs or evidence of protestors smashing and looting to help solve cases.

Many Chinese people welcome the police's resolute move to rein in violence during the protests.

"There is nothing wrong with expressing our patriotic feelings. But I'm against the destructive behaviors," Fang Yan, a woman who has been living in Guangzhou for eight years, told Xinhua.

"The government is doing the right thing, as those who infringe laws must be punished and the safety of law-abiding citizens should be protected," Fang said.

"It's necessary for the government to enhance its safety control over the anti-Japan activities. The so-called 'patriotic' deeds, such as attacks on individuals and properties, in fact hurt our compatriots," said Sun Qiang, a Qingdao resident.

Huang Jingping, a law professor with the Beijing-based Renmin University, said it is the freedom of Chinese people to deliver their opinion to the Japanese government through protests and demonstrations.

"But in a mature society ruled by law, such expression should be legitimate and rational," Huang said.

The Chinese law safeguards all legal properties and lawful businesses, as well as provide equal protection for both Chinese and foreign citizens, he said. "While implementing our own freedom, we should protect and respect the interest of others."

Over the weekend's protests, some clear-minded participants could be seen and heard urging others to refrain from violence, while others volunteered to help in the aftermath of the violence.

Some middle school students in Guangzhou helped clean rubbish and debris left by violent demonstrators outside the damaged Garden Hotel Sunday night, according to the Guangzhou Daily.

The volunteers, who declined to reveal their names, represent the qualities that good citizens should possess, the local newspaper commented.