The Chinese Central Government has sent eight inspection working groups to 16 provincial areas nationwide to prevent the melamine-tainted milk powder, which killed at least six in 2008, from being reclaimed illegally in producing milk products.

Leftovers of milk powder contaminated by melamine were sealed in 2008 and required to be destroyed, but some might have been used as raw materials for diary products illegally in certain areas, according to local police.

Police in Shaanxi Province on Thursday publicized a case on illegal use of leftovers of melamine-tainted milk powder.

An initial investigation showed 10 tonnes of tainted milk powder leftovers were sold to a local diary producer Lekang Company in September and October in 2009. Three suspects were arrested.

Three suspects from the Shanghai Panda Dairy Company were prosecuted in December 2009 on suspicion of using leftovers of melamine-laced milk powder in milk products. Local police said all the company's products had been recalled and caused no serious harms to the consumers.

China's food safety authorities on Feb. 1 launched a 10-day checks for melamine-tainted milk products across the country.

However, the string of problems gave another blow to China's efforts to restore confidence in its dairy products.

The melamine-laced milk products scandal in 2008 killed at least six infants and sickened 300,000 children across the country.

Any illegal practices concerning food safety would be punished severely, an official with the National Food Safety Rectification Office led by Health Minister Chen Zhu said earlier this week.

The quality watchdog of Xi'an, capital of Shaanxi Province, has carried out food safety inspection on 73 batches of different brands of milk products and has not found problems.

The northeastern Jilin provincial government kicked off a milk product safety check at the end of January.

"We must do our best to retrieve and destroy milk products that have quality problems. We can't stand a single pack of such milk powder to appear in market," said Zang Zhongsheng, head of the Jilin provincial administration for industry and commerce.

There is no accurate figure on the amount of problematic milk powder that has not been destroyed in the 2008 milk products scandal. But in the bankrupt dairy producer Sanlu alone, more than 2,000 tonnes of melamine-tainted baby formula was sealed in 2008.

Sanlu, based in Shijiazhuang in Hebei Province, suffered devastating losses and went bankrupt, standing in the spotlight of the melamine-tainted milk products scandal in 2008.

How to destruct the melamine-tainted milk powder was still a tough nut to crack for many local authorities and dairy firms, according to industrial insiders.

A number of experiments had been conducted to find a way to deal with the melamine-tainted powder in Shijiazhuang, but they all failed, according to a insider who declined be named.

"If we use the milk powder as fuels, it would cost much more to clean boilers than burning coal; if we use it as ingredients in cement, we could not get qualified products; if we just bury it, we worry someone might dig it out illegally as the volume is huge," the expert said.

"The milk powder piled like hills and people just don't know what to do," said Zhang Xingkuan, a lawyer who once handle cases on compensation for the scandal victims and frequently visited the dairy firms.

It was more difficult to monitor small dairy firms, which were more inclined to use leftovers of tainted milk to cut cost, according to Wang Weimin, secretary-general of Xi'an Dairy Association.

"They will not do this when milk powder prices are low, but they will do this when milk powder prices soar," he said.

To crack down on such practices, the Chinese government had vowed to investigate the case thoroughly and all factories that use prohibited materials in producing dairy products would be shut down with license suspended and punished severely.