A Chinese central government taskforce has ordered Henan's local authorities to crack down on illegal production and use of clenbuterol, a chemical poisonous to humans.

Traces of clenbuterol have been found in pigs and the practice of adding the chemical to pig food is believed to be widespread in the province, said the taskforce spokesman from the Food Safety Commission Office under the State Council, the cabinet.

Those who deliberately add substances harmful to humans to pig food should be severely punished, said the spokesman who declined to give his name.

Local food safety officers who were negligent in their duties or involved in conspiring with illegal additive producers or pig farmers should also be punished in accordance with the law, the spokesman added.

The taskforce is made up of members from the commission as well as from the ministries of public security, supervision, agriculture, commerce and health, the State Administration for Industry and Commerce and the General Administration of Quality Supervision, Inspection and Quarantine.

The taskforce carried out on-site examinations at local pig farms and slaughterhouses after they arrived in Henan on Sunday.

A subsidiary of China's largest meat processor Shuanghui Group was exposed last week for using clenbuterol-contaminated pork in its meat products.

Clenbuterol is fed to pigs to stop them accumulating fat. It is banned in pig feed in China because it is poisonous to humans if ingested.

The Henan provincial government said in a statement it had started a new round of inspections that would be focused on other additives such as ractopamine and salbutamol, which were used as alternatives to clenbuterol but were neglected in the first round of inspections.