Maritime authorities in Guangxi rescued 26 Vietnamese women and children who were trapped on their boats.
"Six boats sank and 70 other went missing after in flooding," a spokesman with the public security bureau of the city of Fangchenggang told state-run Xinhua news agency.
The region's flood control and drought relief headquarters said heavy rains are still pounding the city of Dongxing.
The headquarters has asked the local government to take precautionary measures to prevent mudslides or other disasters.
One person has been killed so far due to typhoon, the Ministry of Civil Affairs said.
It weakened to a strong tropical storm after sweeping across south China's Hainan province, Guangxi Zhuang autonomous region and north Vietnam, forcing the relocation of tens of thousands of residents.