Quarantine workers have destroyed more than 100,000 chickens in South Korea following the first outbreak of a deadly strain of bird flu in the country in more than a year, an official said Friday.

The Agriculture Ministry plans to speed up the operation to complete the slaughter of some 308,000 chickens near the outbreak site as soon as possible, said ministry official Kim Chang-sup.

The outbreak in Gimje, 257 kilometres south of Seoul, was the first bird flu case involving the lethal H5N1 strain in South Korea since March last year.

Authorities have also banned any unauthorized movement of about 3.6 million poultry on 265 farms within ten kilometres of the outbreak site as a precaution until those birds can be tested for the virus, Kim said.

Seven outbreaks of the deadly virus hit poultry farms across South Korea between November 2006 and March 2007, resulting in the slaughter of about 2.8 million birds.

South Korea declared itself free of bird flu in June last year after reporting no new outbreaks for three months.

At least 238 people worldwide have died from bird flu since 2003, according to the World Health Organization. So far, most human cases have been linked to contact with infected poultry.

Bird flu remains hard for people to catch, but health experts worry the virus could mutate into a form that passes easily among humans, possibly triggering a pandemic.