An outbreak of African swine fever that has cut swathes through China, Vietnam and Mongolia has spread to the isolated country, sparking worries that sick animals crossing the heavily militarized border could devastate the South's US$5.9 billion pork industry.

"We need to focus on preventing wild boars in the North from entering our territory," the South's Prime Minister Lee Nak-yeon said Saturday after visiting a pig farm near the Demilitarized Zone (DMZ) that divides the two countries.

African swine fever is known to be harmless to humans but is fatal to pigs and wild boar and has devastated supply chains in China -- the world's largest consumer of pork -- where authorities have ordered the culling of hundreds of thousands of pigs.

Pyongyang told the World Organisation for Animal Health that 77 out of 99 pigs had died from the disease at a farm near the China border, according to Seoul's agricultural ministry.

The ministry said Friday that the disease is "highly likely" to hit the South, and the government has ordered fences to be erected at farms along the border to prevent possible contact between pigs and wild boars.

Seoul believes Pyongyang raises some 2.6 million pigs across 14 state-run farms. The outbreak could worsen food shortages in the impoverished North, where, according to the World Food Programme, its output last year hit the lowest level since 2008.

In the South, there are about 6,700 pig farms across the country, and pig farming accounts for 40 percent of the total livestock industry.

In 2011, a devastating outbreak of foot-and-mouth disease hit the entire Korean peninsula and resulted in the culling of nearly 3.5 million cattle, pigs and other animals in South Korea alone.

While its bristling fortifications, rolls of barbed wire and trigger happy North Korean troops mean crossing the DMZ can be deadly for humans, the zone has been untouched by development and is a haven for wildlife.

Last October a rare Asiatic black bear was photographed in the zone, Seoul's environmental ministry said.