The tally of children sickened by tainted milk in China jumped to nearly 53,000 as the government vowed to crack down on those responsible for the scandal, which has raised more questions about the safety of the country's food chain.

More than 80 percent of the 12,892 children hospitalized in recent weeks were 2 years old or younger, the Health Ministry said in a statement posted on its Web site late Sunday. The statement said most consumed infant formula from one company, the Shijiazhuang Sanlu Group Co., the dairy at the center of one of China's worst food safety scandals in years.

Another 39,965 children received outpatient treatment at hospitals and were considered "basically recovered," the ministry said.

Over the weekend, the Chinese territory of Hong Kong reported the first known illness outside mainland China — a 3-year-old girl who developed kidney stones after drinking Chinese dairy products. She was discharged from the hospital, a Hong Kong government statement said.

In the two weeks since the government first acknowledged the contamination, it has issued recalls for dairy products from 22 companies after tests turned up traces of the industrial chemical melamine. The Health Ministry said that most of the hospitalized were sickened by Sanlu brand baby formula.

"No cases have been found from ingesting liquid milk," the statement said.

The ministry did not explain the sudden increase in the number of cases, from 6,200 on Saturday, but it suggested health officials were combing through hospital records from May through August to trace the origins of the contamination. The deaths of three infants linked to tainted infant formula occurred in those months, the statement said.

The death of a fourth infant in the far western region of Xinjiang was also linked to tainted formula by the regional health bureau, although the Health Ministry did not include it in its count.

In Hong Kong, parents of the 3-year-old girl took her for a checkup because she had been drinking milk made by Chinese dairy Yili Industrial Group Co. every day for the past 15 months. Yili was among the 22 companies whose products were recalled for melamine contamination.

Beijing has launched high-profile efforts to show it is on top of the crisis, with Premier Wen Jiabao appearing on state-run television Sunday to say diary companies had to show more "social responsibility."

Wen was shown visiting a Beijing hospital where children were having health checks. He also stopped at a supermarket to look at dairy products.

"The government will put more efforts into food security, taking the incident as a warning," Wen said.

"What we are trying to do is to ensure no such event happens in future, by punishing those responsible leaders as well as enterprises. None of those companies lacking professional ethics or social morals will be let off," Wen said, according to the official Xinhua News Agency.

Serious food and product safety scandals have been a feature of Chinese life. The country's image took a beating last year when exports of medicines, toys, pet food ingredients and other products killed and sickened people and animals in North and South America.

The chemical in the dangerous pet food was the same as in the milk scandal — melamine.
At the time, the government promised to overhaul inspection procedures and crack down on companies that took shortcuts.

The crisis has included almost all of China's biggest dairy companies. Their products have been pulled from stores around the country, and in other places such as the autonomous Chinese territories of Hong Kong and Macau.

Singapore announced Sunday that it had found traces of a toxic chemical in a third Chinese-made dairy product. The country's Agri-Food and Veterinary Authority said samples of milk-based White Rabbit brand candy imported from China were contaminated with melamine.

"Retailers and importers have been instructed to recall these products and withhold them from sale," a statement from the authority said.

Japan has also recalled Chinese-made dairy products.

Melamine is used in making plastics and is high in nitrogen, which registers as elevated protein levels in tests of milk. Though health experts believe ingesting minute amounts poses no danger, melamine can cause kidney stones, which can lead to kidney failure. Infants are particularly vulnerable.

Some of the farmers who sell milk to Chinese food companies are thought to have used melamine to disguise watered-down milk and fatten profit margins.