BEIJING: Melamine-tainted dairy products were pulled from convenience store shelves in southern China more than a year after hundreds of thousands of children had been sickened in a massive milk safety scandal, a government spokeswoman said today.

The announcement calls into question the effectiveness of a crackdown launched by Chinese officials to improve product safety after a number of scandals, including the contamination of baby formula in 2008 and the recent discovery of the toxic metal cadmium in cheap jewellery.

Frozen milk products and cartons of milk dating from early 2009 were taken off the shelves after health inspectors tested them and found melamine, said Ling Hu, a Guizhou provincial government spokeswoman.

She said the provincial health bureau was checking to see why the products were not pulled from the shelves earlier. Calls to the Guizhou health bureau ran unanswered Monday. Tainted products from three companies - Shandong Zibo Lusaier Dairy, Liaoning Tieling Wuzhou Food, and Laoting Kaida Refrigeration - were discovered in more than a dozen convenience stores around the province, Ling said.

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

The official China Daily newspaper quoted Wang Dingmian, former chairman of the Guangdong Provincial Dairy Association, as saying tainted milk products recalled at the time somehow made their way back onto the market. He said the latest discoveries of contaminated dairy exposed weak government regulation.

Melamine, which can cause kidney stones and kidney failure, was added to watered-down milk to fool inspectors testing for protein and stretch profits. Both melamine and protein are high in nitrogen.

Dozens of officials, dairy executives and farmers were punished.

Since the scandal broke, China vowed to implement stricter safety measures and step up inspections on the dairy industry. Ling said health officials have continued to target distributors who sell melamine-tainted milk to stores, but some distributors continue to sell it.

Ling said distributors arrested for selling tainted milk likely led authorities to the convenience stores where the contaminated product was found.