East China Sea The East China Sea is a marginal sea east of China . It is a part of the Pacific Ocean and covers an area of roughly . Geography . The East China Sea is bounded on the east by Kyūshū and the Ryukyu Islands of Japan , on the south by the island of Taiwan , and on the west by mainland China and the Asian continent . It is connected with the South China Sea by the Taiwan Strait and with the Sea of Japan by the Korea Strait ; it opens in the north to the Yellow Sea . States with borders on the sea ( clockwise from north ) include : South Korea , Japan , Republic of China ( Taiwan ) and the People ' s Republic of China . Extent . The International Hydrographic Organization defines the limits of the " Eastern China Sea ( Tung Hai ) " as follows : Rivers . The Yangtze River ( Chang Jiang ) is the largest river flowing into the East China Sea . Islands and reefs . There is a cluster of submerged reefs in the northern East China Sea . These include : Nomenclature . During the 19th century , the sea was known as the " Mer de Corée " ( Sea of Korea ) in French . It was one of the three main seas within East Asia , the other two being " Mer du Japon " ( Sea of Japan ) to the north and " Mer de Chine " ( Sea of China , today the South China Sea ) to the south . Until World War II , the sea was referred to as 東支那海 ( " Higashi Shina Kai " ; " East Shina Sea " ) in Japanese . In 2004 , official documents of the Japanese Foreign Ministry and other departments switched to the name 東シナ海 ( pronounced the same ) , which has become the standard usage in Japan . EEZ disputes . There are disputes between the People ' s Republic of China ( PRC ) , Japan , and South Korea over the extent of their respective exclusive economic zones . The dispute between the PRC and Japan concerns the different application of the 1982 UNCLOS , which both nations have ratified . China proposed the application of UNCLOS , considering the natural prolongation of its continental shelf , advocating that the EEZ extends as far as the Okinawa Trough . Its Ministry of Foreign Affairs has stated that " the natural prolongation of the continental shelf of China in the East China Sea extends to the Okinawa Trough and beyond 200 nautical miles from the baselines from which the breadth of the territorial sea of China is measured , " which is applicable to the relevant UNCLOS provisions that support China ' s right to the natural shelf . In 2012 , China presented a submission under the UNCLOS concerning the outer limits of the continental shelf to the UN . Japan , based on UNCLOS , proposed the Median line division of the EEZ . In 1995 , the People ' s Republic of China ( PRC ) discovered an undersea natural gas field in the East China Sea , namely the Chunxiao gas field , which lies within the Chinese EEZ while Japan believes it is connected to other possible reserves beyond the median line . Japan has objected to PRC development of natural gas resources in the East China Sea near an area where the two countries Exclusive Economic Zone ( EEZ ) claims overlap . The specific development in dispute is the PRC ' s drilling in the Chunxiao gas field , which is located in undisputed areas on China ' s side , three or four miles ( 6 km ) west of the median line proposed by Japan . Japan maintains that although the Chunxiao gas field rigs are on the PRC side of a median line that Tokyo regards as the two sides ' sea boundary , they may tap into a field that stretches underground into the disputed area . Japan therefore seeks a share in the natural gas resources . The gas fields in the Xihu Sag area in the East China Sea ( Canxue , Baoyunting , Chunxiao , Duanqiao , Wuyunting , and Tianwaitian ) are estimated to hold proven reserves of 364 BCF of natural gas . Commercial operations began 2006 . In June 2008 , both sides agreed to jointly develop the Chunxiao gas fields . Rounds of disputes about island ownership in the East China Sea have triggered both official and civilian protests between China and Japan . The dispute between PRC and South Korea concerns Socotra Rock , a submerged reef on which South Korea has constructed a scientific research station . While neither country claims the rock as territory , the PRC has objected to Korean activities there as a breach of its EEZ rights . East China Sea in astronomy . Possibly , East China Sea ( " Donghai " in Chinese ) is represented with the star Eta Serpentis in asterism " Left Wall " , Heavenly Market enclosure ( see Chinese constellation ) .