The East China Sea (ECS) is a marginal sea of the Western Pacific Ocean, a geographical concept that is a major geopolitical flashpoint in East Asia. It is bounded by mainland China to the west, the island of Taiwan to the south, and Japan's Kyushu and Ryukyu Islands to the east. The sea connects to the South China Sea via the Taiwan Strait and to the Sea of Japan through the Korea Strait.
The current geopolitical significance of the ECS originated in the late 1960s after a 1968 United Nations survey reported substantial, unexplored oil and gas deposits in the seabed, particularly near the Okinawa Trough. This discovery led to overlapping claims over the sea's resources and sovereignty, primarily between China and Japan, but also involving South Korea and Taiwan.
The mechanism for these disputes is the interpretation of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which both China and Japan have ratified. UNCLOS establishes the framework for maritime zones, including the Exclusive Economic Zone (EEZ), which extends up to 200 nautical miles from a state's baseline. The East China Sea is only about 360 nautical miles wide, meaning the 200-nautical-mile EEZ claims of China and Japan overlap significantly. Japan proposes a median line to divide the EEZ, while China claims its EEZ extends to the Okinawa Trough, based on the natural prolongation of its continental shelf, which is a provision under UNCLOS Article 76.
The most prominent and persistent dispute connects to the sovereignty over the uninhabited islands known as the Senkaku Islands in Japan and the Diaoyu Islands in China. The islands came under US control after World War II and were returned to Japan under the 1971 Okinawa Reversion Treaty. The dispute has recently intensified, with frequent confrontations between Chinese and Japanese coast guard vessels near the islands, such as the incident on July 7, 2026, where both sides accused the other of violating their territorial waters. China also announced an Air Defence Identification Zone (ADIZ) over the area in November 2013. The ECS is a critical area for international law, as the conflicting claims over the EEZ and the Senkaku/Diaoyu Islands test the effectiveness of UNCLOS in resolving disputes.