Bird flu outbreaks first reported early this month have spread to within 70 kilometers of Seoul despite efforts by local quarantine authorities to contain the disease, the government said Tuesday.

The Ministry for Food, Agriculture, Forestry and Fisheries said a chicken farm in Pyeongtaek, Gyeonggi Province reported sudden death of birds on Monday.

"Judging by the way the birds died off and the large numbers involved, there is a good chance that the Pyeongtaek chicken farm has been affected by the avian influenza," said Kim Chang-seob, the ministry's chief veterinary officer.

If it is confirmed that the birds at the chicken farm died from the the virulent H5 strain of the bird flu, it would be a clear sign that the outbreak centered in the Jeolla region in the southwestern part of the country has spread.

Kim said while detailed tests on the suspected Pyeongtaek outbreak won't be confirmed until later in the day, authorities culled the 26,000 birds at the farm.

"If there is confirmation that the H5 strain killed the chickens, all birds raised in poultry farms within 500 meters will be destroyed independent of tests," he said.

In addition to the suspected outbreak in Pyeongtaek, the ministry said three other cases were reported in the Jeolla region. This brings the total of reported cases to 36.

Of these 20 have tested positive for the bird flu virus, with 14 undergoing tests. Of the total two of the sites tested negative for bird flu.

Expert said they do not have not exact numbers of birds that have been culled so far this year, but hinted that it could exceed previous outbreaks.

In the winter of 2003, authorities culled around 5.6 million birds, while in the outbreak of 2006, about 2.8 million birds were destroyed. (Yonhap)