An underground workshop producing fake brand-name condoms was busted after police found clues on an online marketplace.

Two owners of the workshop and more than 10 of their workers were detained in Jinjiang, Fujian province, during a raid on March 29, said an officer surnamed He with the city's public security bureau.

The police announced the details of the case on Tuesday after they finished an initial investigation.

Police confiscated more than 2 million bogus condoms labeled Jissbon, Durex and Contex in the factory and its warehouse. While a knock-off prophylactic is priced at 1 yuan (16 cents), it costs less than 0.2 yuan to produce.

In February, police noticed that prices of brand-name condoms sold at a store on taobao.com, the country's biggest e-commerce marketplace, were unreasonably low, and they bought some products to check, according to a police officer surnamed Xu with the bureau's economic investigation team, which handled the case. After the products were proven to be fake, police took action.

The two bosses, one surnamed Liu, 33, and the other surnamed You, both from Quanzhou, Fujian province, started to produce fake condoms in December.

The duo bought four packing machines and purchased condoms from a factory in Hebei province and packages from Guangdong province.

According to Xu, the production of the fake condoms was so simple that the 50-square-meter workshop could produce 20,000 counterfeits a day.

During the police investigation they discovered two more underground workshops, one in Zhengzhou, Henan province, and the other in Dongyang, Zhejiang province, were purchasing condoms from the same factory in Hebei province.

The raid by the Jinjiang police on March 29 was part of a joint operation. On the same day, police in Henan and Zhejiang provinces broke up underground workshops.

Thirty-seven suspects were arrested, and more than 4.65 million fake condoms with an estimated value of 47.7 million yuan were seized in the joint operation.

The condoms were mainly sold to small supermarkets, adult shops, pharmacies and vendors.