Which gulf in the South China Sea is located between Vietnam and China?

The gulf in the South China Sea between Vietnam and China is the Gulf of Tonkin.

The Gulf of Tonkin occupies the northwestern part of the South China Sea. It is bordered by northern Vietnam on the west and northwest, China’s Guangxi region on the north, and the Leizhou Peninsula and Hainan Island on the east. In Vietnam it is commonly called Vịnh Bắc Bộ, meaning “Northern Bay,” while Chinese usage often calls it Beibu Wan.

The name Tonkin comes from a historical name for northern Vietnam and ultimately refers to Hanoi, once known as the “eastern capital.” The gulf is relatively shallow: most of its seafloor is less than 75 metres deep. Its waters support fishing, shipping, and important coastal ports.

The gulf is also associated with the 1964 Gulf of Tonkin incident, which led to the U.S. Congress passing the Gulf of Tonkin Resolution and helped expand direct American military involvement in the Vietnam War. It should not be confused with the Gulf of Thailand, farther south.