Most of the melamine-tainted milk products recently resurfacing in China have been recalled and destroyed, and none has been put into market or exported, the nation's food safety office said Friday.

"Due to early discovery and timely check, as of now, most of the tainted milk products have been recalled and destroyed, and none has entered the market or been exported," said the National Food Safety Rectification Office in a statement.

Media reports said melamine-tainted dairy products have resurfaced in several Chinese provinces. Explaining why such cases could happen, the office said some producing and processing companies didn't fulfil the responsibilities for food safety and some violators hid tainted milk products or fabricated test reports to dodge inspections.

The office urged related departments at all levels to thoroughly investigate the new cases and severely punish violators.

In 2008, milk laced with melamine led to the deaths of six babies and sickened 300,000 others who had been fed with baby formula made from tainted milk. Melamine is an industrial compound which can give a false positive on protein tests and cause kidney stones.

Melamine-contaminated milk products killed at least six children in 2008 and sickened 300,000

In the recently reported melamine-tainted milk cases, some of the tainted milk products were apparently made of old batches of tainted milk powder slated for destruction but hoarded away instead by dairy firms and later repackaged.