The Gulf of Tonkin is a gulf at the northwestern portion of the South China Sea, located off the coasts of Tonkin and South China. It has a total surface area of 126,250 km2 (48,750 sq mi). It is defined in the west and northwest by the northern coastline of Vietnam down to the Cồn Cỏ district, in the north by China's Guangxi Zhuang Autonomous Region, and to the east by the Leizhou Peninsula and Hainan Island.
China's military has started live-fire exercises in the Gulf of Tonkin - after Vietnam published a map defining what it considers..