Out of 689 pigs awaiting slaughter and processing by Jiyuan Shuanghui Food Co, Ltd, 19 tested positive to having Clenbuterol, an illegal additive poisonous to humans, according to a Jiyuan city government statement.

The city government is also investigating more than 1,300 pig farms and 130 feed and vet drug stores, said the statement. No results have been disclosed yet.

Fourteen people, including seven pig farm managers, six brokers and one purchaser of Jiyuan Shuanghui, were under police custody, according to the provincial government.

At least 6 officials and workers at local animal quarantine stations have been fired or suspended from duty, it said.

All suspected meat products have been taken off shelves, and all feedstuff and meat confirmed to contain the additive have been destroyed.

Further tests are to be performed throughout the province, said Li Mengshun, chief of the provincial animal husbandry bureau.

In Nanjing city, capital of nearby Jiangsu province, the local government suspended operations Thursday of Xingwang Slaughter House after pigs believed to be from Henan tested positive to Clenbuterol.

Authorities also tested pigs in 35 other slaughter plants and 38 pig farms in Nanjing but no tests results were positive.

The tests came after media reports alleging that Jiyuan Shuanghui Food Co, Ltd, purchased pig fed containing Clenbuterol.

Clenbuterol is a chemical that can be fed to pigs to prevent them from accumulating fat. It is banned as an additive in pig feed in China because it can end up in the flesh of pigs and is poisonous to humans if ingested.

According to biological experts, humans can suffer from nausea, headaches, limb tremors and even cancer after eating food containing Clenbuterol.

Jiyuan Shuanghui is under Shuanghui Group, China's largest meat processor with total assets of over 10 billion yuan ($1.52 billion). The Henan-based group has factories in 12 provinces throughout China, producing cooked meat products such as sausage, and also has branches in Japan, Singapore, the Philippines and the Republic of Korea, according to its website.