The six were all arrested in Inner Mongolia on suspicion of involvement in putting the industrial chemical into milk and milk products destined for the factories of major dairy producer Mengniu, Xinhua news agency said.

At least 36 people have so far been arrested for their alleged involvement in the scam in Hebei province, which lies just south of Inner Mongolia and is where the scandal first came to light, the report added.

Melamine is at the centre of a health scare that has rocked China for nearly two months after it emerged the chemical had been illegally put into watered-down milk to give dairy products the illusion of high protein levels.

In the most recent arrests, three of the suspects were detained for mixing melamine with milk, while the others were accused of providing the chemical to the milk producers, Xinhua said.

Four babies have died of kidney failure and more than 53,000 others sickened after drinking tainted milk formula, while contaminated Chinese dairy products have been discovered around the world.

More than 3,600 babies remained in hospital as of Wednesday, the health ministry announced.

The scandal has hit China's dairy industry hard, and continues to escalate around the world as multinationals and countries recall made-in-China milk products.

On Wednesday, the United Nations urged China to modernise its food safety system arguing that an outdated and disjointed approach may have worsened the crisis.

Although at least one Chinese dairy firm knew of the scam for months, it did not immediately report it to local government officials, who in turn delayed passing on the news for nearly a month until after the Aug Beijing Olympics. -- AFP