In a raid Tuesday in the eastern province of Zheijiang, 32 Chinese were detained for making and selling toxic recycled cooking oil believed to have been processed from gutter drains behind the province's restaurants, authorities said.

Police also confiscated 100 tons of "gutter oil." Security official Meng Jianzhu said the operation was part of a crackdown on a wide criminal network of "gutter oil" vendors that for many years has plagued the health of residents in 14 provinces, Reuters reported.

"This case, through a difficult process of investigation, not only struck down a criminal chain of gutter oil producers, but also uncovered hidden details of the offender's greedy and unconscionable production of poisonous and harmful cooking oil," the minister said.

The suspects were seized after a thorough investigation that began in March, after scandalous reports about toxic cooking oil in China accompanied by images of used oil dredged from gutters.

For several years, China's food safety has come under severe scrutiny. Authorities say they have implemented tough punishments to health safety violators, and criminals have vowed not to repeat the offence.

But early in July, 11 Chinese were sentenced to prison and another was placed under suspended death sentence for producing and vending toxic-tainted pork.

In 2008, a worldwide recall was issued by milk manufacturers in China after six children died and almost 300,000 were ill from drinking milk containing high amounts of melamine powder.