Then officials announced that traces of melamine had also been discovered in some samples of liquid milk, including some produced by the country’s leading dairy producers. All tainted dairy products were then ordered off store shelves, and officials have announced many arrests.

At least three infants have died from kidney problems linked to the melamine. Victims also have been found beyond mainland China for the first time, as health authorities in Hong Kong reported over the weekend that an infant had been sickened by melamine in formula from the mainland.

For the government, the scandal is a recurrence of food safety concerns that arose just last year and that officials had pledged to correct with revamped regulatory controls. Last year, thousands of pets in the United States were sickened from food made with Chinese feed laced with melamine. At the time, officials issued regulations banning the use of melamine in food products. Melamine, high in nitrogen, is used to make plastics and fertilizers, but it can be used illegally to artificially inflate protein levels in milk or other foods.

On Sunday, state media carried reports of Prime Minister Wen Jiabao visiting Children’s Hospital in Beijing. “Don’t cry, and it will be over in minutes,” he was quoted as telling a 9-month-old girl undergoing an examination.

The Ministry of Health reported that none of the infants, as yet, had been linked to contaminated liquid milk. Of the nearly 13,000 sickened, officials said 1,579 had already recovered and been released from hospitals. Over all, the ministry said nearly 40,000 infants had been examined.