A fourth Chinese child has died after consuming milk powder tainted with the banned industrial chemical melamine, the government said Thursday.

The latest death was a baby from the far western region of Xinjiang, the official Xinhua news agency reported.

More than 6,000 babies have become sick after drinking the melamine-tainted milk formula. About 20 per cent of the country's supply has been found to be contaminated.

Melamine is used in plastics, fertilizers and flame retardants. It has no nutritional value but is high in nitrogen, which makes the products appear to have higher protein content than they actually do. Suppliers to the dairy companies are believed to have added the chemical to watered-down milk.

Three main brands — Yili Industrial Group Co., Mengniu Dairy Co. and Sanlu — have all been recalled.

Meanwhile, thousands of anxious parents have flooded the country's hospitals to get their children checked as news of the contaminated milk powder has spread.

Fang Sunyi, 28, said she'd fed her three-month-old son the tainted formula since he was born.

"I'm just praying there's nothing wrong with my son," she said. "We first fed him Sanlu, then stopped because that was reported to be bad quality. Then we switched to Yashili, but now there's nothing left. We don't know what's safe anymore and we don't want to take any chances."

Zhang Zhenling, the new chairman and chief executive officer of Sanlu, apologized at a news conference on Thursday.

Police in Hebei province, where Sanlu is based, said so far, 18 people have been arrested and about 220 kilograms of melamine has been confiscated.

The widening crisis has raised questions about the effectiveness of tighter controls China promised after a series of scares in recent years over contaminated seafood, toothpaste and ingredients for pet food.

With files from the Associated Press