Large amounts of rice noodles made with rotten grain and potentially carcinogenic additives are being sold in south China, state press said, in the country's latest food safety scare.

Up to 50 factories in south China's Dongguan city near Hong Kong are producing about 500,000 kilograms of tainted rice noodles a day using stale and mouldy grain, the Beijing Youth Daily said.

The cost-conscious producers were bleaching the rotting rice and using additives including sulphur dioxide and other substances that could cause cancer to stretch 500 grams of grain into 1.5 kg of noodles, it said.

The poor-quality rice had often been reserved for animal feed before food prices began rising dramatically in China in the latter half of 2010, the paper said, citing wholesalers.

Rice noodles, often fried and served with bits of meat and vegetables, are a favourite in southern China.

In recent weeks, a series of tainted food incidents have been reported in the state media as China gears up for New Year and Lunar New Year celebrations - a time when food and alcohol purchases traditionally increase.

Tainted red wine, bleached mushrooms, fake tofu and dyed oranges have all surfaced on store shelves, spooking consumers still wary about food quality after a deadly scandal erupted two years ago over contaminated milk powder.

In Dongguan, a random inspection of 35 rice noodle factories in early December revealed only five of them were making products up to standard, the report said.

The paper did not say what action the government would take against the manufacturers. But the food processing methods used to make the tainted noodles were spreading to other regions as an accepted way to cut costs, it said.

Most of the rice noodles were sold to canteens in thousands of factories in Dongguan, located in China's export-oriented industrial heartland, while about 10 per cent were on sale in city markets, it said.

The Chinese government has come under increasing pressure from its citizens, as well as foreign countries, to improve the standard of its food and medicines.

In 2008, at least six children died and around 300,000 fell sick after consuming powdered milk laced with the industrial chemical melamine, which was added to make products appear higher in protein.

- AFP