A third infant has died in the Chinese powdered milk scandal which has made more than 6,200 babies ill with 158 in a serious condition.

Meanwhile, an official has revealed that the health threat was hidden for at least a month.

The tots drank milk carrying the compound melamine and scores now have "acute kidney failure", the country's Health Minister Chen Zhu said.

A government probe has shown a fifth of the 109 dairy producers checked, including the original supplier Sanlu, had been found to have produced batches of milk adulterated with melamine.

The milk scare has extended beyond the country's borders with China's quality watchdog saying two producers had exported milk powder to Yemen, Bangladesh, Myanmar, Gabon and Burundi and were recalling their products.

China is the world's second-biggest market for baby milk powder, and Sanlu has long dominated it. Based in Shijiazhuang, capital of the north Chinese province of Hebei, it is 43 per cent owned by New Zealand dairy giant Fonterra - which believes the milk may have been sabotaged.

Sanlu last week halted production and announced a big recall. But government officials acted only after the New Zealand government pressed Beijing.

Yang Chongyong, a vice governor of Hebei, said Shijiazhuang officials had delayed reporting the poisonings throughout August - when Beijing was hosting the Olympic Games.

He said: "It should be said that the Shijiazhuang government did not announce to society in a timely way this major food safety incident."

Sanlu kept quiet for even longer, Yang said.

He added: "We know that before they reported the problem to the Shijiazhuang government on August 2 they had already covered up many of the facts."

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