By Louise WattBEIJING -- Chinese are trying to hurt Japan economically for leverage in a bitter dispute over contested islands, turning to angry protests and calls for boycotts of Japanese businesses, abetted in part by China's government. Sporadic protests in China over the past week became larger and at times violent and spread to at least two dozen cities over the weekend. Protesters torched a Panasonic factory and Toyota ( TM) dealership in the eastern port of Qingdao, looted a Heiwado Co. department store in the southern city of Changsha and ransacked Japanese supermarkets in several cities. Though larger numbers of police imposed more order on demonstrations Sunday, they fired tear gas to subdue rowdy protesters in the southern city of Shenzhen. In nearby Guangzhou city, protesters broke into a hotel that was next to the Japanese Consulate and damaged a Japanese restaurant inside. Japan has demanded that China ensure the safety of Japanese citizens and businesses. "Unfortunately, this is an issue that is impacting the safety of our citizens and causing damage to the property of Japanese businesses," Japanese Prime Minister Yoshihiko Noda told NHK, Japan's public broadcaster, on Sunday. U.S. Defense Secretary Leon Panetta said Sunday he is concerned that island disputes in the Asia-Pacific region could spark provocations and result in violence that could involve other nations, such as the United States. > > Bull or Bear? Vote in Our Poll While it urged protesters not to resort to violence, China's government has also encouraged the use of economic pressure in the dispute over Japan's control over the East China Sea islands, called Senkaku in Japan and Diaoyu in China. China's National Tourism Administration ordered travel companies last week to cancel tours to Japan over the weeklong National Day holiday in early October and promised to compensate any businesses for costs they could not recover, said a lawyer who saw the written order and asked not to be identified because the document is not for public use.