Health authorities must step up efforts to trace hidden melamine-tainted milk products that should have been destroyed, in the wake of large batches of contaminated products turning up this month in two provinces, a Health Ministry official said Tuesday.

"From the problematic milk powder found in Qinghai, we can see that we need to do more in this work," Chen Rui, a vice director with the Ministry of Health's food safety department, told a press conference.

Food safety incidents must be thoroughly investigated and the perpetrators must be severely punished, he said.

Melamine added to milk products can make the protein content seem higher. In the melamine scandal of 2008, the industrial chemical caused the deaths of six babies and sickened 300,000 others who had been fed with baby formula made from tainted milk.

China's government has repeatedly ordered all tainted products to be destroyed, but reports of tainted items have continued to emerge.

In the latest discovery, Chinese police authorities found 64 tons of raw materials for making milk powder and 12 tons of processed powder tainted with melamine at a factory in the far-western province of Qinghai.

Some packages of milk formula also tested positive for excessive melamine content in northeast China's Jilin Province. The tainted products were among 900 kg of milk formula that were found to be produced by a plant with suspected falsified production licenses.

Chen said about 25,000 tons of melamine-tainted dairy products had been destroyed since 2008.

He said authorities were still investigating the Qinghai case, and promised to publish progress in the investigation in a timely manner.