Beijing - Chinese medical staff examined some 53,000 infants and hospitalized nearly 13,000 for problems linked to the consumption of powdered milk laced with the chemical melamine, state media reported on Monday.

As the fallout from the scandal continued, the government said an an investigation confirmed that the Sanlu company, the producer of much of the tainted milk powder, had covered up problems of melamine contamination for months.

The government on Monday sacked the mayor of Shijiazhuang, the capital of the northern province of Hebei, where Sanlu is based.

Sanlu had reported problems to the city government on August 2 but Shijiazhuang officials did not inform the provincial government until September 9, China Central Television said in its evening news broadcast.

Sanlu had "covered up for months the contamination of its baby formula products", the official Xinhua news agency late Monday quoted an official investigation as saying.

The agency gave no details of the investigation, but earlier reports said Sanlu knew about the contamination of milk powder in March.

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

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

The health ministry said 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.

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

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

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

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

Health inspectors last week 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.

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. (dpa)