An African swine fever outbreak is spreading widely in Vietnam and is hurting the local farming industry, forcing the culling of three times the number of hogs culled last year, the government said on Thursday.

"The outbreak is evolving in a complicated manner," the government said in a statement. "It is threatening to spread on a large scale."

The outbreak has this year spread to 2,275 areas, in 57 out of the country's 63 cities and provinces, the government said, adding that the authorities have so far this year culled 230,000 hogs.

African swine fever is harmless to humans but often fatal to pigs. It originated in Africa before spreading to Europe and Asia and has killed hundreds of millions of pigs.

Vietnam reported its first African swine fever cases among its hog herd in February 2019. The disease forced the culling of around 20% of its hog herd and doubled domestic price of pork as of early last year.

The outbreak subsided during the rest of last year and early this year, allowing the country to rebuild its hog herd.