Two new chemicals with the same function as clenbuterol hydrochloride - an illegal drug used to produce lean pork - were detected in recent food safety checks, local watchdogs said yesterday.

Salbutamol and ractopamine were found in 5 percent of pork products, while clenbuterol was detected in 1 percent of samples, officials from the Shanghai Food and Drug Administration said yesterday.

Local authorities have intensified checks and established a blacklist of farms feeding the chemicals to pigs and banning them from the Shanghai market.

Ingesting large quantities of these slimming drugs can damage people's hearts, with fatal consequences.

Pork tainted with clenbuterol substitutes was found during self-checks by abattoirs and wet markets and in government spot checks.

"The new chemicals are replacements for clenbuterol and are being fed to pigs to keep their meat lean," said Gu Zhenhua, director of Shanghai FDA's food supervision department.

"Thanks to new technology, since the beginning of the year we can perform instant checks for these chemicals and know the results within 20 minutes," Gu said.

Previously, laboratory tests took 48 hours, Gu said.

"Any local pig farms found feeding pigs slimming drugs will be reported to the police immediately, and if the farms are in other regions, we will inform the food safety authorities and police there," Gu said.

Pig farmers who feed their stock slimming chemicals face up to seven years in prison. The punishment is more severe if the practice results in death or severe injury among consumers.

Shanghai residents consume about 3 million pigs a year. About 20 percent come from local pig farms, while the remainder are from areas including Henan, Jiangsu, Zhejiang, Jiangxi and Shandong provinces.

Shanghai has established a computerized system covering all 16 abattoirs and eight wholesale markets which tracks each pig through the sales and processing chain.