Timeline: China milk scandal

Melamine-tainted milk products have been found on sale in China, more than a year after thousands of children became ill in a huge safety scandal.

Products made by three different firms were found to contain melamine and have now been removed from supermarkets in Guizhou province, officials say.

Melamine can be added to watered-down milk to make it appear to have a higher protein content.

Six children died and some 300,000 became ill from tainted milk in 2008.

If ingested in sufficient quantities, melamine can cause kidney failure and kidney stones.

The companies involved in the latest recall blamed the contamination on milk powder they had bought as a raw material to add to their products, state media reported.

An official involved in the 2008 investigation told China Daily the powder may been part of that recalled batch which was still circulating on the market.

"There were still some leftovers in the dealers' hands that nobody cared about," said Wang Dingmian, former chairman of the Guangdong Provincial Dairy Association.

Mr Wang said the government's regulation of milk products was too weak and that companies should be required to test every batch they used.

China says 21 people have been convicted over the 2008 scandal, including milk producers, traders and executives of the Sanlu milk company.

In November 2009, two people were executed for making and selling hundreds of tonnes of melamine-tainted milk products.