Which department should be in charge of illegally turning residential areas into food processing plants?

Illegal construction in residential areas shall be ordered by the construction administrative department of the people's government at or above the county level to dismantle it within a time limit, and the owners and property users shall be fined between 1,000 yuan and 5,000 yuan, and the decoration enterprises shall be fined between 5,000 yuan and 50,000 yuan; If it is not removed within the time limit, the construction administrative department of the people's government at or above the county level may apply to the people's court for compulsory execution.

People's Republic of China (PRC) building law

Article 64 Anyone who, in violation of the provisions of this Law, starts construction without obtaining a construction permit or without approval of the commencement report, shall be ordered to make corrections, and those who fail to meet the conditions for starting construction shall be ordered to stop construction and may be fined.