A popular Japanese brand of chocolate-filled cookies bearing the images of cartoon koala bears is the latest Chinese-made food product confirmed to be tainted by an industrial chemical, the government in the southern Chinese territory Macau said Thursday.

The amount of melamine in the Koala's March cookies made by Lotte China Foods Co. was 24 times the safety limit, the Macau government said in a statement.

Calls to Beijing-based Lotte China Foods and its Hong Kong distributor after office hours went unanswered.

The company is a member of Tokyo-based conglomerate Lotte Group.

The food safety crisis in China started with melamine-tainted infant formula, which has sickened more than 50,000 Chinese children, but has spread to dairy and other food products. Most recently, tests in Hong Kong and Singapore confirmed a famous Chinese candy brand was tainted.

The tests in Macau also found melamine in milk made by leading Chinese dairy Mengniu Dairy Group Co. and milk powder made by Nestle.

Mengniu's products were already confirmed to be contaminated earlier.

The amount of melamine in the Nestle product was within safety standards. The Swiss manufacturer has said its Chinese-made products are safe.

Meanwhile, Hong Kong reported a fifth child has developed a kidney stone after drinking tainted Chinese milk.

The latest patient, a 10-year-old boy, is hospitalized in stable condition, the Hong Kong government said in a statement.

The boy drank two packs of Mengniu milk each day from 2005 to 2007, then switched to milk from another leading Chinese dairy, Yili Industrial Group Co., in 2007, Health Department spokeswoman Eva Wong said.

He also started taking two Yili milk tablets each day since March, Wong said.

The Hong Kong government also said Thursday it will start checking fresh milk imports from China for melamine.

Chinese suppliers trying to boost output are believed to have diluted their milk while adding melamine because its nitrogen content can fool tests aimed at verifying protein content.

Health experts say ingesting a small amount of the chemical poses no danger, but melamine, usually used to make plastics and fertilizer, can cause kidney stones and lead to kidney failure. Infants are particularly vulnerable.