Japan on Tuesday admitted it was slow to detect an outbreak of foot-and-mouth disease as the affected region declared a state of emergency after culling more than 110,000 animals.

The disease, which sickens animals but rarely affects humans, was confirmed in late April, three weeks after the first animals fell ill, triggering a beef and pork export ban and threatening Japan's premium Miyazaki beef sector.

Prime Minister Yukio Hatoyama, who on Monday announced special aid for the region, conceded that "there may have been certain (problems) in terms of having done everything we could to prevent the spread" of the disease.

"The government will have to be united in working to avert further expansion of the infection," he said.

Hideo Higashikokubaru, the governor of Miyazaki, declared a state of emergency and warned that "we are facing the risk that the disease will spread beyond" his prefecture on the southwestern island of Kyushu.

By Tuesday, animal health workers had culled more than 114,000 cows, buffalo, pigs and goats to contain the disease that had spread to 126 farms.

Japan on April 20 suspended its beef and pork exports after detecting suspected cases of foot-and-mouth disease in a cattle herd, in what was soon confirmed as the island-nation's first outbreak in a decade.

Officials said Tuesday that cases of animals falling ill in late March were initially misdiagnosed as normal diarrhoea.

"There was a mistake in that the initial diagnosis did not conclude it was foot-and-month disease," Hiroshi Nakai, the chief of the National Public Safety Commission, said in a television interview.

The epidemic has forced the cull of scores of prized breeding bulls, leaving just six of them, now kept in isolation, to inseminate cows to produce the tender and highly marbled beef from the region.

Foot-and-mouth disease affects cloven-hoofed animals, also including sheep, goats and deer. It is rarely transmitted to humans but spreads easily between animals, causing them pain and often killing their young.

The UN Food and Agriculture Organisation late last month urged countries to step up vigilance against foot-and-mouth disease following the cases in Japan and an outbreak in South Korea since early April.

Japan, a net food importer, exports only around 500 tonnes of beef a year - including some 35 tonnes of the premium Miyazaki beef, a sought-after delicacy for its intense marbling with mostly unsaturated fat.