In the latest alert, authorities said more than a dozen stores in southern Guizhou province were found to be selling contaminated products.

Officials said the products may have been recalled after the earlier scandal but had found their way back on to the market.

Chinese authorities vowed to step up screeing in the wake of recent scandals [AFP]
However the products were made in March and April last year, months after the government declared the melamine scare over.

Melamine is normally used in the manufacture of plastics and fertilizer, but can disguise milk that has been watered-down by making the diluted milk appear to contain more protein than it actually does in quality control tests.

If consumed by humans, it can cause kidney stones to develop and potentially kidney failure.

Dozens of officials, dairy executives and farmers were punished following the 2008 scandal and two were sentenced to death.

The scandal also led to the bankruptcy of Sanlu, once one of the biggest dairy firms in China.

In the wake of the scare Chinese authorities vowed to implement stricter consumer safety measures and step up inspections on the dairy industry in particular.