Chinese doctors examined some 53,000 infants and hospitalized nearly 13,000 for problems related to the consumption of powdered milk contaminated with the chemical melamine, state media reported on Monday.

A total of 12,892 infants were hospitalized and 39,965 others were taken to outpatient clinics across China for illnesses believed to be linked to baby milk powder, the official China Daily quoted the health ministry as saying.

Four babies had died and 104 were seriously ill with kidney problems, while 1,579 babies were discharged from hospital after treatment, the newspaper said.

Most of those under treatment had consumed baby milk powder made by the Sanlu firm and 99.2 per cent of them were under three years old, it said.

The government on Monday approved the resignation of Li Changjiang, its top official for quality supervision, over the baby milk scandal, the official Xinhua news agency said.

Li was replaced by Wang Yong, a senior official from the State Council, or cabinet, the agency said.

China's top leaders over the weekend urged officials across the country to respond to the growing scandal after one government department said it had received more than 100,000 complaints about dairy products.

Vice Premier Li Keqiang on Saturday visited a hospital treating babies stricken by melamine-laced milk powder in the northern province of Hebei, where Sanlu is based and many of the cases of melamine-related illness were recorded.

The State Administration for Industry and Commerce has launched a nationwide inspection of all dairy producers, wholesalers and retailers.

The administration issued an urgent circular ordering local officials to verify the qualifications of all dairy businesses and ensure that unlicensed ones were closed down.

It had received 106,143 complaints and refunded the cost of 304.38 tons of dairy products by Saturday morning, reports said.

Health inspectors on Friday said they found melamine in some liquid milk and yoghurt sold by three leading dairy producers - Yili, Mengniu and Bright Dairy.

Traces of melamine were also found in liquid milk sold in Hong Kong by Swiss-based global food giant Nestle.

But the company said the milk, which was produced in the eastern Chinese city of Qingdao, appeared to have been contaminated by its packaging.

Nestle said in a statement that none of its dairy products sold in mainland China were contaminated with melamine.

Melamine is used as a binding agent and coating for particle, fibre and laminated board in furniture. It is also used to make fertilizer.

Hebei police have formally charged 18 people who sold melamine to milk producers or sold contaminated milk, and detained at least a dozen other milk dealers, melamine traders, company officials and local quality supervisors.

Government officials said Sanlu knew about the contamination of milk powder with melamine since March but didn't order a national recall of the powder until last week.

The World Health Organization (WHO) expressed satisfaction on Sunday with the response of the Chinese government in containing the spread of the tainted infant milk.