The 1990s-era building in Henan province collapsed suddenly on Friday afternoon in a project which involved adding more levels to the two-storey building, state media said.
Video footage broadcast on state television showed firemen picking through the rubble using their hands in the search for survivors.
The local government in Wuyang county, where the accident occurred, had called off the search by Saturday, the official Xinhua news agency said. Nine of the injured were in serious condition, it said.
The booming Chinese economy has spurred a wave of new infrastructure and construction projects, but corruption is common and strict enforcement of regulations is often lacking.
In 2011, 12 workers who were building an underground parking lot in northeastern China were killed when a concrete ceiling collapsed onto them.