Melamine contamination has been found in 23 milk products imported into Vietnam from China, officials said Tuesday, intensifying consumer worries about tainted milk products.

Five more products tested positive for the industrial chemical, which is usually used in making plastics and fertilizers. So far authorities have found 23 contaminated products after testing 400 samples of milk and milk products, Vietnam's vice-minister of health Cao Minh Quang said.

About 300 tonnes of products, mostly imported from China, have been recalled, said the ministry's chief inspector, Tran Quang Trung.

China pledged Monday to improve food safety and authorities detained six more people in the country's contaminated milk scandal. The head of China's quality watchdog said the country was also stepping up checks on its exports.

On Tuesday, Liberia joined the growing list of dozens of countries that have banned imports of Chinese milk products amid worldwide concern about tainted milk powder from China.

Milk formula containing the industrial chemical melamine has been blamed for killing four infants and sickening more than 54,000 children in China since mid-September.

The Canadian Food Inspection Agency has issued warnings about two products imported from China because they tested positive for melamine. One product is White Rabbit brand candy, a popular Chinese confection.

The candy is normally available for sale at retail stores throughout Canada in a variety of flavours, the agency said.

The other product was Nissin Cha Cha Dessert that was made with Yili Pure Milk. It was distributed in Ontario, Alberta and British Columbia.