HANOI, Vietnam - Vietnam says melamine contamination has been found in five more milk products imported from China.

Vietnamese health officials say they have now found contamination from the industrial chemical in 23 of 400 samples of milk and milk products.

Tran Quang Trung, chief inspector for Vietnam's Health Ministry, says about 300 tonnes of contaminated products, mostly imported from China, have been recalled.

Quang says the department's top priority is to protect the health of people, especially children who are especially susceptible to melamine poisoning.

Many Vietnamese consumers have stopped buying milk products since reports of the contamination surfaced, and that is starting to hurt local dairy producers.

Nguyen Thi Mai, a dairy farmer in Phu Dong village just outside Hanoi, said she has had to give away or throw away milk since factories stopped buying it six days ago.

"I don't know what is melamine, but it's killing us," she said.

China pledged to improve food safety Monday 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.

Liberia banned imports of Chinese milk products Tuesday amid worldwide concern about tainted milk powder from China.

In a radio announcement, acting Commerce Minister Frederick Norkeh called the ban "a precautionary measure" taken because of what he called reports that the contaminated milk was being shipped to African countries. He did not provide details.

There have been no reports of tainted milk sold in Liberia, he said. It was not immediately clear if Liberia has imported Chinese milk products in the past.

The ban was expected to be temporary and would take effect immediately, Norkeh said.

Dozens of other countries worldwide have banned Chinese milk products in recent weeks. 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.