South Korea said Wednesday it is speeding up efforts to cull poultry around farms infected with highly pathogenic bird flu amid growing concerns over the virus spreading nationwide.

The country has culled 5.59 million birds as preventive measures since reporting the first farm-related case in late November, according to the Ministry of Agriculture, Food and Rural Affairs.

Chickens accounted for 3.5 million, followed by quails with 1.2 million and ducks with 880,000.

Local authorities slaughtered poultry within a 3-kilometer radius of infected farms.

South Korea has reported 16 cases of highly pathogenic bird flu from farms. South Jeolla Province accounted for six, and Gyeonggi and North Jeolla provinces accounted for three infections each.

There were also cases from the provinces of South and North Chungcheong, along with South Gyeongsang.

Authorities are currently investigating a suspected case from an egg farm in Hwaseong, south of Seoul. The farm was raising 90,000 chickens.

Highly pathogenic avian influenza is contagious and can cause severe illness and even death in poultry.

The country reported this year's first highly pathogenic avian influenza case from wild birds in late October. Since then, a total of 29 cases have been found from wild bird habitats nationwide.

Authorities are currently investigating seven suspected cases from wild birds. (Yonhap)