A wild mandarin duck captured in Cheonan, South Chungcheong Province, on Monday has been confirmed infected with the H5NI avian influenza, according to the agriculture and environment ministries.

It is the first time in seven months since late March that South Korea has reported a case of a highly pathogenic strain of the bird flu in a wild bird. 

Disease experts have locked down access along the river where the duck was discovered, setting up checkpoints and allowing no personnel or vehicles within a 500 meter radius. Farms located within a ten kilometer radius will be subject to a three-week standstill order and thorough testing and sterilization procedures.

The agriculture ministry on Wednesday raised its bird flu alert level from the second lowest to the highest level in a four-tier system.

The last time the government raised its alert level for avian flu to "serious" was from last November to March this year.