Melamine was found in eggs produced by China's largest egg producer.
Chinese authorities said Wednesday that they were investigating how eggs came to be contaminated with the same industrial chemical at the center of a milk scandal that sickened thousands of babies, as more tainted eggs turned up in Hong Kong and the mainland.
The action follows the pulling from some store shelves of a brand of chicken eggs produced by China's leading egg processor, Dalian Hanwei Enterprise Group, after Hong Kong food safety regulators found excessive levels of melamine in eggs from the company.
The widening food scare has exposed the inability of Chinese authorities to keep the food-production process clean of melamine, the chemical that sparked the recent dairy crisis, despite official vows to raise food safety standards.
China's fresh eggs are mainly exported to the Chinese territories of Hong Kong and Macau, while processed egg products are also sold to Japan and the US, according to a February egg market report on the Agriculture Ministry's website.