Rainfall was expected to intensify through Thursday in the Guangxi region, the weather bureau said, according to Xinhua.
Flooding caused by torrential rains has killed at least 19 people in southern China, the official Xinhua news agency said on Wednesday.
In the Guangxi region, which borders Vietnam, week-long downpours triggered floods in six cities, killing 12 and affecting more than 570,000 people, Xinhua said, citing the regional emergency management department.
It added that houses collapsed and crops were damaged.
Rainfall was expected to intensify through Thursday, the regional weather bureau said, according to Xinhua.
In neighbouring Guangdong province, seven people were killed and one was missing as heavy rain destroyed roads and toppled houses, the report added.