Rescuers were trying to reach the workers trapped since Friday morning in the flooded mine in the Inner Mongolian city of Wuhai, the official Xinhua news agency said on Sunday.
"The rescue team said the chance of survival is thin," Xinhua said, without elaborating.
Seventeen miners had been rescued. The flood occurred after miners had either dug into an abandoned mine shaft filled with water or hit an underground spring, it said.
Police had detained both the chairman and head of the mine.
The mine had been closed by authorities last week because of concern over its ventilation, but it had been secretly reopened by management, Xinhua said.
Separately, two miners trapped underground after a blast in a mine in the northern province of Shanxi on Friday were confirmed dead, bringing the toll from that accident to 36, Xinhua said.
Chinese mines have the worst safety record in the world, with accidents killing thousands of workers every year.