"One floor of the G+4 structure was found to be illegally constructed," the official said.
There were trade licences for 136 shops in the market, he said.
City Mayor Sovan Chatterjee had said after a visit to the fire-ravaged market complex in Sealdah area that the KMC will inquire if any part of the building was illegally constructed.
Security guards in such markets, they said, will be trained in fire-fighting operations.
Besides, KMC will make arrangements for installing CCTVs in all its 46 markets, particularly those located in congested areas, the sources added.