Amid growing concern about food safety problems across the country, customers are most concerned about dairy products, leading to a "black market" in human breast milk.

While some mothers have turned to imported formulas to feed their babies, others are selling their own breast milk online to make some extra money and help mothers who are not producing enough milk of their own.

On some of the most popular shopping websites like taobao.com, mothers who claim to have an over-supply of milk are selling fresh human breast milk frozen in special storage bags.

Prices range from 39 yuan ($6) to 100 yuan, depending on the freshness of the milk. Most of these milk donors are from big cities such as Shanghai, Beijing and Shenzhen. But most sellers only accept deals within their own city so that the milk will not deteriorate while being delivered.

One seller sold five 200-milliliter bags of milk in two days, and a buyer left a comment saying that the price, though high, was "value for money" compared with imported formulas.

The new product soon attracted wide attention and invited a nationwide media blitz questioning the freshness and purity of the milk. This publicity caused most sellers to drop their offers on taobao.com.