Milk and other foods thought to be contaminated with the chemical melamine have been removed from sale in the south of the country.

In the original incident melamine had been used to bulk out powdered milk and increase profits for suppliers. Several people have been executed after an inquiry into the affair.

Tainted products from three companies, Shandong Zibo Lusaier Dairy, Liaoning Tieling Wuzhou Food and Laoting Kaida Refrigeration, were found in more than a dozen convenience stores around Guizhou province.

Laoting Kaida Refrigeration was among companies named in the original melamine scandal in 2008, when six children died and 300,000 were poisoned after drinking baby formula contaminated with melamine, an industrial chemical used in the manufacture of plastics and fertiliser.

Investigators found that melamine, which can cause kidney stones and kidney failure, had been added to watered-down milk to fool inspectors testing for protein. Both melamine and protein are high in nitrogen. Dozens of officials, dairy executives and farmers were punished.

China vowed to implement stricter safety measures and step up inspections on the dairy industry. Health officials have continued to crack down on distributors who sell melamine-tainted milk to stores, but some distributors, wrongly assuming that the government has scaled back its crackdown, continue to sell it.

The case was the latest example of how difficult it has been for the government to ensure the safety of food products. Earlier this month, government officials said the Shanghai Panda Dairy had been under a secret investigation for nearly a year before announcing they had been producing melamine-tainted milk.