Beijing: China reported on Monday the death of a second infant from tainted milk powder in a growing scandal that left hundreds more ill but only led to a product recall after the New Zealand government raised the alarm.

Two traders were arrested for selling up to 3 tonnes of contaminated milk a day, police reported.

The latest death blamed on infant milk powder made by the Sanlu Group was in Gansu province, a poor northwest region where the first infant fatality linked to the chemical-laced milk was also reported, the official Xinhua news agency said.

One of the infants was a five-month-old boy who died in May. The other was an eight-month-old girl who died in July after her parents removed her from hospital, health ministry official Wang Yu told a news conference.

"The family refused an operation to insert a catheter and abandoned treatment," Wang said, without explaining why.

By Monday morning, 1,253 children had been diagnosed with illnesses linked to the milk powder, with 340 still in hospital and 53 "relatively serious", Vice Minister of Health Ma Xiaowei told the news conference. At the weekend, officials said 432 children were ill from the milk powder.

Milk powder producer Sanlu, 43 per cent owned by New Zealand dairy giant Fonterra, last week halted production after investigators found the chemical compound melamine in its powder was causing kidney stones and complications in infants.