Tens of thousands of Chinese took to the streets in at least a dozen cities on Sunday in what appeared to be coordinated anti-Japan protests that saw Japanese cars smashed and restaurants attacked in several areas. The widespread protests — a rare occurrence in China — were sparked by news on Sunday that 10 Japanese activists had raised their flag on the disputed Diaoyu or Senkaku islands in the East China Sea.

The Chinese Foreign Ministry on Sunday hit out at the activists’ move, which followed a trip by around 150 Japanese lawmakers and activists to the disputed islands.

“The illegal actions of the Japanese rightists have violated China’s territorial sovereignty, and senior officials from the Foreign Ministry have lodged solemn representations to the Japanese ambassador to China,” said spokesperson Qin Gang in a statement reported by the official Xinhua news agency.

“The Japanese side should properly handle the current issue and avoid seriously damaging the overall situation of China-Japan relations.”

Sunday saw the unprecedented spread of anti-Japan protests across at least a dozen cities — mainly in eastern China, which suffered most during the Japanese occupation — and incidents of violence directed at Japanese restaurants and parked cars.

The protests appeared to have taken place with the permission of the authorities. Protests are usually disallowed by the government. Police forces in the cities where gatherings took place appeared not to disperse the protesters.

The State-run Xinhua news agency reported protests in Guangzhou, Shenzhen and Hangzhou in southern China, and Shenyang, Harbin and Qingdao in the northeast. In Guangzhou, protesters staged a sit-in outside the Japanese Consulate carrying banners calling on China to “defend its territory”.

While official reports said several thousand people had gathered, photographs circulating online from some cities, such as Shenzhen and Chengdu in south-western Sichuan, showed gatherings of at least tens of thousands of people in each city. By the afternoon, incidents of violence were reported, with photographs of smashed cars and broken windows of Japanese restaurants circulating online. So far, there have been no reports of casualties.

The gatherings appeared to have been organised online, and initial posts on the popular Twitter equivalent Sina Weibo that called for people to gather were not censored by the authorities. Usually, calls to protest on just about any domestic matter, from land rights to political issues, are deleted by censors.

By Sunday evening, however, censors began to delete some photographs and messages, suggesting that the authorities were caught off-guard by the size of the crowds and the intensity of protests that they had initially appeared to tolerate.