East China Sea, an arm of the Pacific Ocean, located off the eastern coast of Asia. The sea is bounded on the east by Kyūshū Island and the Ryūkyū Islands and on the south by Taiwan and the Taiwan Strait; it merges with the Yellow Sea on the northwest. The most important ports on the sea are Shanghai, China, and Nagasaki, Japan. The principal river draining into the sea is the Yangtze. The sea floor averages 350 m (1,200 ft) and drops to a maximum depth of 4,600 m (15,000 ft). The sea covers an area of 1,249,000 sq km (482,000 sq mi).