JINAN -- East China's Shandong Province has banned the sales of turbot containing excessive amounts of carcinogens that were purposefully fed banned chemicals by fish farmers.

Shandong, a major turbot producing area, has urged local authorities to ban feeding turbot and other fish banned medicines and foodstuffs in a bid to ensure food safety.

It has also called on local authorities to trace contaminated fish and crank up inspection efforts in the raising, transportation, storage and sales of turbot and other fish.

The Shanghai food and drug administration announced Friday it detected excessive residue including nitrofuran and chloromycetinin in 30 samples of turbot. The chemicals are known cancer causing agents.

Fish markets, shopping malls, and hotels have stopped selling turbot following government warnings.

Due to their low resistance to disease, the fish, introduced from Europe in the 1990s, are sometimes fed large quantities of medicinal supplements, which leave harmful, cancer causing residue in their flesh.

The State Food and Drug Administration has ordered local offices and authorities in coastal areas including Shandong, Jiangsu, Hebei, Zhejiang, Fujian, Guangdong, Liaoning, and Tianjin to closely monitor the case and aquaculture.

China is currently saddled with severe food security problems as problematic food products continue to be banned. Recent cases include parasite-infested snails, steroid-tainted pork and ducks that were fed a cancer-causing dye to make their yolks red.