The toxic chemical melamine is probably being routinely added to Chinese animal feed, state media has reported after several brands of Chinese eggs were found to contain the chemical.
BBC correspondents say the unusually frank reports in news outlets are an admission that contamination could be widespread throughout the food chain.
"The feed industry seems to have acquiesced to agree on using the chemical to reduce production costs while maintaining the protein count for quality inspections," the state-run China Daily said in an editorial.
"We cannot say for sure if the same chemical has made its way into other types of food," the newspaper added.
Melamine is a chemical used to make plastics. It was found in dairy products including baby formula made in China. About 54,000 babies became ill and at least three died as a result of drinking melamine-tainted products in the past two months.