BEIJING (Reuters) – Inner Mongolia in northern China has detained four people for forging documents and illegally selling and transporting pigs from a province that has been hit by African swine fever, said the region’s animal husbandry bureau late on Wednesday.

This comes after a slaughterhouse in the capital Hohhot discovered four pigs infected with the highly contagious disease that has been spreading rapidly across the world’s top pork producer since its discovery in August.

The Hohhot slaughterhouse reported discovering the disease to the government earlier this week.

The husbandry bureau said in an online statement that the pigs came from Liaoning province in China’s northeast, where swine fever first appeared. Liaoning is banned from supplying pigs to other regions, as are all areas affected by the disease.

Traders in Tieling city in Liaoning were able to truck 96 pigs to Inner Mongolia after an official veterinarian in the autonomous region provided illegal quarantine certificates in return for 8,000 yuan ($1,163.81), the bureau said.

Four people including the veterinarian have been detained, and the traders in Liaoning are being pursued, it said.

It was not possible to contact the suspects and it was not known whether they had retained legal representation.

The husbandry bureau urged government departments to step up supervision of veterinarians and law enforcement, and to severely crack down on illegal activities.

China has reported 20 cases of African swine fever since early August, and it has banned the transport of live pigs from 16 provinces that have reported outbreaks or border provinces with outbreaks to limit the spread of the disease.

(Reporting by Dominique Patton; Editing by Tom Hogue)