Padang ekspres.net-Photos from the southwestern city of Chengdu and the central city of Zhengzhu showed hundreds of people marching with banners and signs protesting Japan's claim on what China calls the Diaoyu islands. Japan calls them the Senkaku islands.
Japanese retailers Ito-Yokado and Isetan said protesters in Chengdu broke windows and showcases in their stores, Kyodo News agency reported.
China's state-run Xinhua News Agency said more than 2,000 people protested in Chengdu and thousands of college students gathered in the northern city of Xian.
The report was in English only. The protests were not reported in Chinese-language state media, and many comments and photos were quickly removed fom mainland websites.
Protests in China are often quickly shut down or heavily controlled. It was not clear whether the organizers had permission to demonstrate Saturday.
Foreign Ministry spokesman Ma Zhaoxu said in a statement on the ministry's website late Saturday that China and Japan were important neighbors to each other and should resolve their differences through dialogue.
"It is understandable that some people expressed their outrage against the recent erroneous words and deeds on the Japanese side," Ma said. "We maintain that patriotism should be expressed rationally and in line with law." The Chinese demonstrations appeared to be in response to online reports about a planned protest in Tokyo, where about 2,500 people held flags and marched near the Chinese Embassy to protest China's claim to the islands. Some also called for the release of Liu Xiaobo, the Nobel Peace Prize-winning Chinese disident who is serving an 11-year prison sentence for subversion.
Ma said China had contacted Japanese officials to "express serious concern" over the Tokyo protest, according to a separate statement.
At the time, tensions were high over a collision between a Chinese fishing boat and two Japanese coast guard ships near the islands in the East China Sea. China repeatedly demanded the return of the detained fishing boat captain. Japan eventually released the captain, but Beijing shocked Tokyo by demanding an apology.
Earlier this month, the tensions seemed to calm after the prime ministers of the two countries held an impromptu after-dinner meeting in the corridor of an Asia-Europe summit.
Police in the Chinese cities of Chengdu, Xian and Zhengzhou would not confirm Saturday's protests, saying they would not talk to the media.
Associated Press Writer Eric Talmadge in Tokyo and researcher Henry Hou in Beijing contributed to this report.