SHANGHAI  Chinese regulators said Friday that they were widening their investigation into contaminated food amid growing signs that the toxic industrial chemical melamine has leached into the nation’s animal feed supplies, posing health risks to consumers throughout the world.

The announcement came after food safety tests earlier this week found that eggs produced in three provinces in China were contaminated with melamine, which is blamed for causing kidney stones and renal failure in infants. The tests have led to recalls of eggs and to consumer warnings.

The reports are another serious blow to China’s agriculture industry, which is already struggling to cope with its worst food-safety scandal in decades after melamine-tainted milk supplies sickened over 50,000 children, caused at least four deaths and led to global recalls of goods produced with Chinese dairy products earlier this fall.

The milk crisis is fueling worldwide concerns about food from China. In Hong Kong, food safety officials announced this week that they would begin testing a broader variety of foods for melamine, including vegetables, flour and meat products. On the mainland, Shanghai and other cities are moving aggressively to test a wide variety of food products for melamine, including fish and livestock feed, according to the state-run news media, which in recent days has carried multiple reports on melamine in animal feed.