A total of 41 miners were working in the Batian coal mine when the flood hit, but 13 escaped, the report said.
A rescue operation is in progress and the whereabouts of the trapped miners were not immediately known.
Three workers were trapped by flood in an iron ore mine in Guangxi Zhuang Autonomous Region in the south of the country on Saturday night, Xinhua also reported. Rescue workers were still trying to free them Sunday afternoon.
Last year 2,631 Chinese miners were killed, according to official statistics, but independent labour groups say the true figure is likely to be much higher as many accidents are believed to be covered up.