Over 200 rescuers were pressed in to remove the debris at the accident site near the village of Houshan in Wu'an City of northern China's Hebei Province, rescue headquarters said.
The isolated building near the village collapsed early on Monday morning.
Sixteen construction workers of the Fengshanbao Iron Mine, were staying in the building for the night when it went down.
The subsidence depth was estimated at about 15 to 20 meters, and the complicated geological conditions and the building's narrow foundation made the rescue work even harder, state run Xinhua news agency reported.