BEIJING (AP) - 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.