The bureau said its investigation is continuing.

According to the Shanghai administration for industry and commerce, more than 32,000 steamed buns have been taken off the shelves at supermarkets and impounded by the administration.

The administration ordered local stores and supermarkets to check steamed buns from other manufacturers and stop selling them if they have any doubts about their quality.

Officials from the bureau said it will also carry out tests on other brands supplying steamed food as part of the investigation.

Li Yuanping, a spokesman for the General Administration of Quality Supervision, Inspection and Quarantine, China's top quality watchdog, said it has ordered the quality supervision authority in Shanghai to thoroughly investigate the case and severely punish those responsible for any wrongdoing.

"We must gravely crack down on illegal activities and will never relent," Li was quoted as saying by Xinhua News Agency.