BEIJING (AP) — China has reported a new outbreak of African swine fever that is threating the country's vital pork industry.

The Ministry of Agriculture and Rural Affairs reported Friday the disease had been detected on a farm in Yongzhou in the central province of Hunan, where 4,600 pigs were being raised.

Although just 171 of the pigs had died and 270 were found sick, ministry regulations require all pigs on an affected farm must be culled and disposed of and the area quarantined and decontaminated.

First detected in August, the disease has killed more than 1 million pigs in China, prompting restrictions on shipments of most of China's 700 million swine, even healthy ones.

That has disrupted supplies of pork, China's staple meat, to big cities while prices collapsed in areas with an oversupply of pigs that farmers are barred from shipping to other provinces. It also resulted in additional stress on pig farmers already beset by rising feed costs from Beijing's tariff fight with President Donald Trump.

African swine fever doesn't affect humans but is highly contagious in pigs.

Dozens of cases have been detected over recent months in at least 20 provinces.

It wasn't clear how the virus reached China, but it was found to be genetically similar to versions in Russia, Poland and Georgia.

The outbreak could cause longer-term disruption if farmers respond to lower prices and higher costs by raising fewer pigs, leading to shortages and higher prices.

The government maintains stocks of frozen pork in case of shortages but has yet to say whether any will be released this year.