A report by state media says some offenders are leaving infected feed in sties and are even using drones to spread contamination.

Pork prices have spiked as a result of the disease, and gangs can profit by getting around controls to smuggle meat across provincial boundaries.

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Chinese criminals have been exploiting the country's African swine fever crisis by intentionally spreading the disease to force farmers to sell their pigs for a low price before smuggling the meat and selling it on as healthy stock, state media has reported.

Sometimes the gangs spread rumours about the virus, which is fatal to pigs, but in more extreme cases they are using drones to drop infected items into farms, according to an investigation by the magazine China Comment, which is affiliated to state news agency Xinhua.

The disease has reduced the country's pig herds by over 40% due to mass culls designed to stop it spreading further. The resulting shortages have seen pork prices more than double, providing opportunities for the criminals to exploit.

The magazine's report said that the gangs tried to spread panic among farmers to force them to sell their livestock at a discount rate.

Sometimes they spread rumours about the disease spreading in the locality and may even leave dead pigs on the side of a road to make farmers believe the infection is spreading. In some extreme cases, the gangs even placed infected feed inside local pigsties, the report said.

"One of our branches once spotted drones air dropping unknown objects into our piggery, and later inspection found [the] virus in those things," a farmer manager told the reporters.

Once they have bought the pigs, the gangs then smuggle the animals or their meat to other areas where prices are higher, despite a ban on transporting pork or livestock between provinces to control the spread of the disease.

The profit margin can be as much as 1,000 yuan (US$143) per pig, so dealers have been stockpiling funds for bulk purchases.

"However many pigs you have, we are taking them all," the story quoted a dealer as saying.

In the southwestern province of Yunnan alone, the authorities have already intercepted 10,000 live pigs, some infected with the virus, that were destined for other provinces.

The report said police believed that one gang had smuggled 4,000 pigs from the province in one day. It said that smugglers had been bribing inspectors and faking quarantine certificates to smuggle the animals across provincial borders.

In one such case in Lichuan, a city in the central province of Hubei, the disease spread through the area after a vet forged certificates for infected animals.

The smugglers are trying to profit from a spike in prices that has seen the cost of meat rise from about 20 yuan per kilogram to a high of 52.30 yuan last month.

Between now and the Lunar New Year holiday in late January, when demand is expected to peak, prices could rise to between 65 and 75 yuan per kilo, according to Nomura.