Twenty more pigs have tested positive in initial checks for foot-and-mouth disease at two farms in central South Korea.
Tens of thousands of pigs have already been slaughtered because of outbreaks of the disease.
The outbreak comes just weeks before the World Cup, co-hosted by South Korea and Japan. The nearest World Cup cities are Suwon, 24 miles to the north of the affected region, and Daejeon, 50 miles to the south.
Japan has raised concerns about the possible spread of the disease when tourists visit the two countries during the tournament. South Korea has called the concerns "groundless" as the contaminated area is far from World Cup venues.
Yesterdays, four cases of the disease were confirmed in nearby districts, prompting workers to start slaughtering 23,000 livestock, mostly pigs, at 16 farms in the region.
It is government policy to slaughter all livestock in farms within 500 metres from where a case of the infection is found to prevent the epidemic from spreading.
AP