Japan protested to China on Sunday after Chinese coastguard ships sailed into territorial waters of disputed islands in the East China Sea, Tokyo said. Four Chinese vessels entered the waters surrounding the islets, called the Senkaku in Japan and the Diaoyu in China, at about 10am local time, according to Japan’s coastguard. Why are Chinese vessels sailing off the Diaoyus? According to Beijing’s envoy, they’re after ‘big fish’ They left the territorial waters within two hours, the coastguard said. A statement by China’s State Oceanic Administration said the coastguard vessels conducted a patrol in waters around the Diaoyu Islands yesterday. The vessels are CCG 2401, 2101, 2502 and 35115. China has been conducting such patrols on a regular basis. The two countries are locked in a long-running dispute over the uninhabited, Tokyo-controlled islets. Japan has routinely complained that China is escalating regional tensions by regularly sending ships to the island chain despite repeated protests from Tokyo. Boiling point: Can China and Japan find a way to ease rising tensions over the East China Sea? Yesterday, Tokyo lodged a protest to China’s foreign ministry through its embassy in Beijing, saying the islands are “an inherent territory of Japan”, while Prime Minister Shinzo Abe’s office beefed up its team in charge of monitoring Chinese ships, a government official said. Tokyo has lodged at least 32 protests through diplomatic channels this year over what it says have been a total 31 days of intrusions by Chinese vessels in the territorial waters. Improving but still fragile: China’s Li Keqiang strikes balanced line on ties after meeting Japanese envoy Last week, Premier Li Keqiang called on business leaders and former government officials from China and Japan to make joint efforts to consolidate public support for improved relations. He said bilateral relations had seen improvement, but the foundation of the relationship was still not solid. China is also involved in maritime disputes in the South China Sea through its claims over most of the area, despite partial counter-claims by the Philippines, Brunei, Malaysia, Taiwan and Vietnam.