Melamine, a toxic chemical, is used to fool quality inspectors testing milk for protein levels [EPA]

Chinese police have seized around 26 tonnes of milk powder tainted with melamine, state media reported, three years after infant formula contaminated with the same chemical killed six babies.

The powder was purchased by an icecream maker in Chongqing, a southwestern city, for use in pastries and icecream.

However the product had been stored in a warehouse and had not yet been used, a report in the Global Times newspaper said on Wednesday.

Five suspects, including company managers at three firms, have been detained and three could face criminal charges, the paper said, but did not identify their suspected roles in the contamination.

The powder was said to have been produced in Inner Mongolia and sold to a third company in 2009.

Other seized batches have been described as old stocks that were hidden when they should have been destroyed.

China's food sector has been hit by food poisonings and toxin scandals, despite a number of government crackdowns.

In 2008, at least six children died and nearly 300,000 fell ill from powdered milk laced with melamine, an industrial chemical added to low quality or diluted milk to fool inspectors checking for protein levels.

Adding melamine and water to milk and milk products makes the products appear to have the correct protein content, but leads to health problems such as kidney stones and kidney damage.

A recent spate of new problems prompted the State Council, China's Cabinet, to last week order a renewed crackdown on the illegal foodadditives.

So far this year, authorities have uncovered sales of drug-tainted pork, bean sprouts treated with a carcinogenic chemical compound, and old bread treated with sweeteners and dye to make it seem fresh.