South Korea's foot-and-mouth outbreak on Thursday spread deeper into the mainland from an island west of Seoul despite massive quarantine efforts to contain the disease, officials said.

The agriculture ministry confirmed cattle at a farm in Chungju, 147 kilometres (90 miles) south of Seoul, tested positive for the highly contagious disease in the eighth outbreak nationwide.

Local authorities in Chungju began culling over 12,000 animals including cattle, pigs, deer, goats and sheep at the infected farm and four others nearby, Yonhap news agency said.

The latest outbreak indicated the virus was spreading further away from the epicentre on Ganghwa Island, 60 kilometres west of Seoul, where a total of six cases have been reported since the first outbreak on April 9.

Prime Minister Chung Un-Chan called in agriculture, health and other ministers to discuss measures to stop the spread of the disease, aides said.

"The country's foot-and-mouth disease alert will remain at the current 'Orange' level but all countermeasures will be taken at the highest 'Red' one," Vice Agriculture Minister Ha Young-Je told journalists.

Quarantine officials believe humans could be responsible for having spread the virus to the farm in Chungju, according to Yonhap.

On Tuesday, authorities confirmed infection at a farm in Gimpo, 30 kilometres west of Seoul, in the first outbreak outside Ganghwa. Gimpo is a mainland region linked by a bridge to the island.

Gimpo officials have culled almost 200 cattle at the infected farm and three nearby farms, and have banned the movement of over 74,000 animals at 362 farms within a 10-kilometre radius.

Authorities culled some 30,000 animals at 227 farms on Ganghwa to limit the spread of foot-and-mouth.

The virus can spread rapidly between animals but is rarely transmitted to humans.

South Korea ordered a halt to pork and beef exports in January when an outbreak of the disease was confirmed in Pocheon, northeast of Seoul.

Outbreaks in 2000 and 2002 cost South Korea an estimated 450 billion won (400 million dollars).