It added eight of the 29 miners working at the location had already been rescued.
Staff were carrying out upgrading works at the site when disaster struck.
Chinese state-controlled broadcaster CCTV reported that 12 miners were on one platform, with eight more on a second platform, and the last worker is currently trapped in an escape route where water had originally entered.
“The working platform with 12 people is 1,200 meters (3,900 feet) from ground level and the underground terrain is complex, making rescue difficult,” CCTV said.
Coal mines in China are among the world’s most dangerous, with explosions and gas leaks a regular occurrence.
Mining accidents in eastern Shandong province in January and the southwest city of Chongqing in December killed more than 30 miners.