The South Korean government has declared all parts of the country "at risk" and is taking extraordinary measures after a highly pathogenic strain of the bird flu was reported last Friday at a poultry farm for the first time in more than two and a half years.
The minister of agriculture, Kim Hyeon-soo, said in a briefing on Sunday that the virus, of the type H5N8, was most likely transmitted to ducks at a local farm by migratory birds from Siberia.
The minister said the virus is not currently being transmitted to humans.
Response headquarters have been set up at local governments across the country, which are carrying out disinfection work and monitoring for violations.
Those breaking the rules, the government says, will face strict punishment.