FILE PHOTO: Piglets are seen by a sow at a pig farm in Zhoukou, Henan province, China June 3, 2018. REUTERS/Stringer

BEIJING (Reuters) - Criminal gangs in China are faking outbreaks of African swine fever on farms free of the disease and forcing farmers to sell their healthy pigs at sharply lower prices, the agriculture ministry said on Friday.

The gangs are taking advantage of a highly contagious disease that has spread across much of the country and disrupted the world’s biggest pork market.

The scam involves dumping dead pigs on farms and then spreading rumors that the farms are infected with African swine fever, which is often fatal for pigs but harmless for humans.

The gangs then pressure farmers to sell their hogs at lower prices, violating farmers’ rights and affecting normal pig production, the Ministry of Agriculture and Rural Affairs said in a statement.

The ministry did not give more details but it urged anyone who witnessed such activities to alert the authorities.

“All localities should be vigilant and actively guard against it,” it said.

Up to half of China’s breeding pigs have either died from African swine fever or been slaughtered because of the spreading disease, twice as many as officially acknowledged, Reuters reported last month.