"We are most concerned about the H5 and H7, as these two can infect people and fowl," said Huang Kwo-ching, director of the animal health inspection division at the Council of Agriculture.

"We are now carrying out testing at poultry farms within a 3 km (1.9 mile) radius of the area," he said by telephone.

The single sample of H7N3 was found in marsh land in the southern city of Tainan, the Council of Agriculture said in a statement, adding that no dead birds were found in the area.

It was the second time the strain has been detected in Taiwan. The first case of H7N3 was discovered in the outskirts of Taipei in April, said the official.

The H7N3, which can potentially be transmitted to humans, was first detected in turkeys in Britain in 1963 and made one of its last known appearances in poultry in Canada in April and May 2004, according to the World Health Organisation and World Organization for Animal Health.

According to the WHO, H5 and H7 viruses are the only avian influenza subtypes that are implicated in outbreaks of highly pathogenic disease.

The WHO recommends aggressive control measures, including culling of infected and exposed poultry, for these two subtypes even when the virus initially shows low pathogenicity.

Taiwan has not experienced a major outbreak of H5N1. Last month, the island found only its second case of the deadly strain since 2003, in birds smuggled in a container ship from China.