China has detained 900 people for crimes including selling rat and fox meat as beef and mutton, the public security ministry said, in another blow to the nation's food safety.

News of the three-month operation, which related to meat products, added to a string of scandals that have galvanised public concern over food safety in China, from recycled cooking oil to dangerous chemicals in baby milk powder.

Altogether there were "382 cases of water-injected meat, fake mutton and beef, diseased meat, toxic and harmful meat products", the ministry said on its website on Thursday.

"Nine hundred and four suspects were arrested, more than 20,000 tons of various types of fake or inferior meat products were confiscated."

The crimes ranged from sellers in eastern Jiangsu province making fake mutton from fox, rat and chemicals, and others in southwestern Guizhou province mixing hydrogen peroxide solution with chicken claws.

The scandal was widely discussed by users of China's popular Sina Weibo microblog.

"Anything can be done once humanity is gone," said one user.

"We are nearly immune to hundreds of poisons, should we thank these fantastic businessmen?" wrote another.

China's top court on Friday announced its first ever detailed guidelines for the punishment of food-safety related crimes, the state-run China News Service reported.

The crimes listed included supplying meat from animals which died of illness, selling food with excessive amounts of chemical additives, and falsely advertising food products, the report said, citing China's Supreme People's Court.

The public security ministry said the sting on the toxic meat was part of a wider probe into food safety issues, from the discovery in March of thousands of dead pigs floating down a Shanghai river to the problem of "gutter oil".

Cheap recycled cooking oil is available nationwide made illegally from leftovers scooped out of restaurant drains.

One of China's worst food safety scandals hit in 2008 when the industrial chemical melamine was found to have been illegally added to dairy products, killing at least six babies and making 300,000 people ill.

In another recent incident, US fast food giant KFC was hit by controversy after revealing some Chinese suppliers provided chicken with high levels of antibiotics, in what appeared to be an industry-wide practice.