The chemical was found in Heinz DHA+AA Vegetable Formula Cereal and in Silang House-brand steamed potato wasabi crackers produced by Kam Tai Co., the Center for Food Safety said.
Both were manufactured in mainland China, it said in a statement.
The center said it has asked importers to recall the two products and urged retailers to stop selling them.
Pittsburgh, Pennsylvania-based Heinz ordered a recall of the baby cereal as a precautionary measure following the Hong Kong government's announcement, it said in a statement on its Web site.
It said all other Heinz products were found to be melamine-free after extensive testing.
The contaminated product is less than 1 percent of the company's baby food sales in Hong Kong and contains only trace amounts of melamine, Heinz said.
A man who answered the phone at Kam Tai in Hong Kong declined to comment.
China's food safety crisis started with melamine-tainted infant formula, 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.
Melamine-laced milk has been blamed for the death of four babies and for sickening more than 50,000 children in mainland China. Six children in Hong Kong and Macau have been found with kidney stones after drinking tainted Chinese milk.
Earlier, supermarkets in Hong Kong stripped shelves of a popular Chinese-made cookie brand after Macau authorities found excessive amounts of melamine in the product.
Macau's Health Bureau found the amount of melamine in the Koala's March brand made by Japan's Lotte China Foods Co. was 24 times the safe limit.
An official at Lotte (China) Investment Co. Ltd. in Shanghai said previous inspections had not shown any problems.
"The range of the inspections covered all the products sold domestically, including the bear chocolate-filled cookies mentioned in the report. The outcome was all fine," said Guo Hongming, a legal assistant in Lotte Shanghai's corporate planning department.
"But now that it tested positive in Macau, we find it necessary to do the inspections all over again," she said.
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.
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 levels.
