SEOUL (AFP) - South Korea imposed on Monday a 12-hour lockdown on poultry farms in three provinces to curb a spreading bird flu outbreak, banning the movement of animals, people and vehicles.

More than 640,000 poultry have already been slaughtered since the outbreak was first detected on January 16 at a duck farm in Gochang, 300 km southwest of Seoul.

The H5N8 strain of bird flu has since been identified in 17 other farms, with tests being carried out in 22 others, and a further 810,000 poultry have been identified for slaughter.

The 12-hour travel ban on poultry farmers and other members of the industry, including vets, took effect at 6:00am Monday in Gyeonggi province - which surrounds Seoul - and the provinces of South and North Chungcheong.

The South Korean capital was not included in the lockdown.

During the 12-hour period, local officials will oversee disinfection operations at all farms in the region.

It is the first bird flu outbreak in South Korea since 2011, when more than six million poultry were culled at about 280 farms.

The lockdown comes amid fears that the mass movement of people during the coming Lunar New Year holiday will fan the spread of the disease.

Millions of people travel to their hometowns - many in rural areas - to meet relatives and pay respects at ancestors' graves during the traditional holiday, which this year lasts from January 30 to February 2.

"What holiday? I'm too busy protecting my ducks," one poultry farmer in Gochang told the local Maeil Business Newspaper.

"This catastrophe is overshadowing and unnerving the whole village. I told my children never even dream of coming home this year," another Gochang resident said.