A court case against a gang accused of a $15.6-million "gutter oil" scam began in China Wednesday, state media said, in what appears to be the latest stage of a crackdown on reprocessed cooking oil.

The trade in "gutter oil" -- which normally refers to cooking oil illegally made by reprocessing waste oil or by dredging up leftovers from restaurants and then marketing it as new -- is one of a number of major food scandals in China.

Health authorities in China launched a crackdown on the practice a year ago which resulted in the arrests of more than 100 people.

Twenty people were charged at the court in the eastern Zhejiang province with manufacturing and selling fake and substandard products, and manufacturing and selling toxic and hazardous food, according to the Xinhua news agency.

The scam generated 99.2 million yuan ($15.6 million) since it began in December 2007, the state news agency said, quoting a statement from the Intermediate People's Court in Ningbo.

The court did not hand down a verdict at the hearing, it added.

"Gutter oil" has been deemed by authorities as unsafe for consumption because it contains carcinogenic substances.

Special operations to stamp down on the practice of reprocessing used cooking oil had shut down 13 underground workshops and seized over 3,200 tonnes of the oil by April this year.