SEOUL, Dec. 20 (Xinhua) -- Almost 20 million ducks and chickens have been culled in South Korea as a highly pathogenic strain of avian influenza (AI) spread rapidly nationwide, Yonhap news agency reported on Tuesday.

According to the Ministry of Agriculture, Food and Rural Affairs data cited by Yonhap, the number of poultry destroyed for the bird flu infection reached 19.11 million as of Monday.

The first case was reported at a farm in Haenam county, South Jeolla province, the country's southwestern region, on Nov. 16.

The figure means about 600,000 chickens and ducks have been slaughtered per day in the past month, and the number is expected to increase further in the near future.

The H5N6 virus is spreading at an alarming speed, confirming 204 farms nationwide as infected areas.

It marked the worst, fastest-ever infection since 19.37 million birds were destroyed for 669 days between 2014 and 2015 for the H5N8 virus outbreak.

The agriculture ministry has raised the AI crisis level to the highest in its four-tier system.

Egg prices have surged recently as 17.8 percent of total layer chickens, which lay eggs, or 12.44 million chickens, have been culled for the H5N6 virus infection. Egg prices rose 11 percent in the past week.

Discount outlets reportedly began to restrain the number of eggs which one person can buy at a time amid the supply shortage.