Vietnam has culled nearly 10% of its pig herd to contain an African swine fever outbreak that has started hitting large-scale industrial farms, the government said in a statement on Tuesday.

Earlier outbreaks have appeared mostly at small household farms but have now started to occur at larger industrial operations, including Phu Son Farm in Dong Nai province near Ho Chi Minh City, the statement said.

“This is a very worrying sign as these farms have tens of thousands or hundreds of thousands of pigs each and therefore the damages would be significant,” the government said in a statement posted to its official website.

African swine fever, which is deadly to pigs but harmless to humans, was first detected in Vietnam in February and has spread to farms in 60 of the country’s 63 provinces, according to the statement.

Authorities have this week culled hundreds of pigs at Phu Son Farm, home to more than 18,000 pigs, Bach Duc Luu, the deputy head of Vietnam’s Department of Animal Health, said on Tuesday.

A representative of the farm, owned by Phu Son Livestock Joint Stock Co, declined to comment.

Phu Son Farm, founded in 1976, is one of the oldest of its kind in Vietnam. The farm supplies pork mostly to Dong Nai province and neighbouring Ho Chi Minh City.

Nationwide, Vietnam has culled more than 2.8 million pigs in the outbreak, the government said in the statement, up from 2.5 million pigs a week ago.

In March, the United Nations Food and Agriculture Organisation (FAO) advised Vietnam to declare the outbreak a national emergency, but officials said last week they had no plans to do so.

Heavy rains in southern Vietnam could help the virus spread further, Luu said.

Nguyen Van Long, head of epidemiology at the animal health department said that it was “only a matter of time” before the disease spreads to all 63 provinces.

Pork makes up three-quarters of total meat consumption in Vietnam, a country of 95 million people where most of its 30 million farm-raised pigs are consumed domestically.

The country’s pork industry is valued at around 94 trillion dong ($4.03 billion), and accounts for nearly 10% of Vietnam’s agricultural sector.

African swine fever was first detected in Asia last August in China, the world’s largest pork producer, where the disease is expected to reduce the herd by up to 200 million pigs this year.