Two persons were also reported missing as the debris covered about 200 square metres.
Local officials said the accident occurred early today in Mayong Township, Dongguan, and the workers appeared to have been using the temporary structure as a dormitory.
So far, 14 people have been rescued and were admitted to hospitals, the city's information office said.
An earlier statement issued by the office said 69 people had managed to escape the mishap when the collapse happened.
More than 200 firefighters were searching for those still buried, and 40 fire engines are on hand.