A senior United Nations bird flu expert has gone to North Korea to try to prevent the spread of the virus.
South Korea is taking preventative measures at the border
North Korea confirmed on Saturday that bird flu had been detected in several farms near the capital, Pyongyang.
State media said hundreds of thousands of chickens had been destroyed to prevent the virus from spreading, and no humans had been affected.
The UN has also sent diagnostic kits to help the North Koreans determine if the birds died from the deadly H5N1 strain.
This strain of bird flu has killed almost 50 people since its resurgence in South East Asia in December 2003.
Hans Wagner, a senior official from the UN's Food and Agriculture Organization, flew to Pyongyang on Tuesday, and will be joined by two other experts from China and Australia in the coming days.
H5N1 BIRD FLU VIRUS
Principally an avian disease, first seen in humans in Hong Kong, 1997
Almost all human cases thought to be contracted from birds
Isolated cases of human-to-human transmission in Hong Kong and Vietnam
"They will look at the strategies being set up by the government and also bring some supplies," FAO spokesman Diderik de Vleeschauwer told Reuters news agency.
South Korea's Yonhap news agency reported on Tuesday that the North Korean authorities were struggling to control the outbreak, and the disease was spreading quickly.
Analysts warn that the virus could wipe out the poverty-stricken country's chicken industry.
Before the bird flu outbreak, poultry production was one of the few growing sectors in North Korea. The number of poultry was estimated at 25.5m in 2004, about two times higher than in 1997.