The disease has spread to farms run by over 23,300 households, or 30 percent of all farming households in the capital city, according to the Hanoi People’s Committee.

The disease is tending to spread to large-scale farms, it said.

Around 1.9 million pigs are being raised in Hanoi, the country's second biggest herd after the southern province of Dong Nai's 2.5 million.

60 of Vietnam’s 63 cities and provinces have seen African swine fever outbreaks so far, with only Ninh Thuan in the south-central region, Tay Ninh near Ho Chi Minh City and Ben Tre in the Mekong Delta being spared to date. About 2.83 million pigs have been culled, causing losses worth estimated at over VND3.6 trillion ($154.77 million).

African swine fever first appeared in northern Vietnam in early February and quickly spread across the northern and central regions before reaching the south in May. Hanoi was hit in early March.

The virus is shed in blood, saliva, tears, nasal secretions, urine, feces, and secretions from the animal's genital tract. Pigs can thus get the infection by contact with many different infected sources, mainly other infected pigs, pork and other pig-derived products but also any other contaminated object, according to the Food and Agriculture Organization. While the disease is incurable, it does not affect humans.

Data from the World Organization for Animal Health shows that as of June 20, 14 countries and territories were suffering from new or ongoing outbreaks of the disease: Belgium, Hungary, Latvia, Moldova, Poland, Romania, Russia, Ukraine, mainland China, Hong Kong, North Korea, Laos, Vietnam and South Africa.