Qiong Zhou Fu Zhi (Chorography of Qiongzhou Prefecture) by Ming Yi (Qing Dynasty)

In Qiong Zhou Fu Zhi, the book written by Ming Yi in the Qing Dynasty (AD 1636-1912), the tract of seas controlled by the navy of Yazhou in the Daoguang Era was described as "spreading in the east from Dong'ao Port in Wanzhou to Sigengsha in Changhua County in the west, covering 1,000 li; adjoining the oceans of Siam and Champa in the south, Danzhou in the west and Haikou in the east." This indicates that back then the Chinese navy patrol had reached the southern sections of the South China Sea.