The Xinhua News Agency said Monday a note passed through a rescue shaft Sunday night reported the fate of the other 10 remains unknown.
The handwritten note said four of the workers were injured and that the condition of others was deteriorating because of a lack of fresh air and an influx of water.
Managers of the operation were detained after they failed to report the accident for more than a day. The mine in Qixia, a jurisdiction under the city of Yantai in Shandong province, had been under construction at the time of the blast, which occurred Jan. 10.
More than 300 workers are seeking to clear obstructions while drilling a new shaft to reach the chambers where the workers were trapped and expel dangerous fumes.
"Keep on with the rescue efforts. We have hope, thank you," read the note, written in pencil on notebook paper and posted on Xinhua's official website.
China's mining industry has a reputation for skirting safety requirements amid massive demand for coal and precious minerals, although increased supervision has reduced the frequency of accidents that used to claim an average of 5,000 miners per year.
Two accidents in the southwestern megacity of Chongqing last year killed 39 miners, prompting the central government to order another safety overhaul.