SHIJIAZHUANG - Sixteen people remained missing as of Wednesday morning after a factory building collapsed on Monday in North China's Hebei province, according to rescue headquarters.

Over 200 rescuers were excavating debris at the accident site near the village of Houshan in Wu'an city, said the rescue headquarters.

The isolated building near the village collapsed early on Monday morning.

The buried, all construction workers for Fengshanbao Iron Mine, were staying in the building for the night.

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, according to headquarters.

An investigation into the cause of the collapse is under way.