Sanlu did not go public until September 11.

Dairy crisis timeline

According to CCTV, Sanlu first learned on June 1 that its milk had been tainted with melamine. Five babies were hospitalised, suffering from kidney stones

But it was not until August 2 that Sanlu began to do anything to prevent the sale of the milk, notifying the local government in Shijiazhuang that its milk was tainted.

On August 6 Sanlu pulled the milk from its distributors, but did not announce a public recall.

Finally, on September 11, Sanlu publically recalled 700 tonnes of its baby formula, while the government vowed serious punishment for those involved.

"During these eight months, the company did not inform the government and did not take proper measures, therefore making the situation worse," CCTV reported, citing an investigation by the State Council, China's cabinet.

Melamine, a toxic chemical used in the manufacturing of plastics and fertiliser, has been blamed for sickening some 54,000 babies and young children.

To date at least four have died, while another 104 remain in serious condition.

Speaking to Al Jazeera on Tuesday, Dr Hans Trodesson, country representative for the World Health Organisation (WHO) in Beijing, said meetings with Chinese officials had demonstrated the government was determined to ensure the scandal was not repeated.

"We have clear indication that they are taking it very seriously and they are also consulting us on how it could be prevented in the future," he said.

But, he added, "food safety is always a work in progress - you never get a water-tight system."

Melamine is believed to have been added by suppliers trying to cut costs because the chemical's high nitrogen content can help disguise watered-down milk, making it appear to have the same protein content as regular milk.

Resignation

Tests since the scandal first broke have shown traces of melamine in infant formula and other milk products from 22 of China's dairy companies.

Some 54,000 children have been stricken in the scandal across China [AFP]
The latest revelations in the scandal came as the head of China's food safety watchdog resigned over his organisation's failure to contain the safety scare.

Li Changjiang quit on Monday as head of China's General Administration of Quality Supervision, Inspection and Quarantine.

Li had held the post since 2001 and last year pledged to lead a wide-ranging overhaul of the monitoring system following a series of high-profile product safety scares.

At the time a series of improvements were announced, including the setting up of a national food recall system.

In a show of the government's determination to improve product safety, in July last year the former head of China's food and drug agency was executed after being found guilty of taking bribes in exchange for letting fake medicine into the domestic market.