Areas within 3 km of a farm in north China's Hebei Province, the site of an H5N2 bird flu outbreak in poultry, were confirmed to have been sealed off, according to local government.

The disease killed 4,000 chickens raised at the farm in Baoding City after they showed symptoms of suspected avian flu on Dec. 17, according to the Ministry of Agriculture.

The National Avian Influenza Reference Laboratory on Saturday confirmed the epidemic was caused by the H5N2 avian influenza virus after testing samples collected at the farm.

Local authorities have sealed off and sterilized the infected area, where a total of 125,700 chickens have been culled and safely disposed of to prevent the disease from spreading.

Bird flu, or avian influenza, is a contagious disease of animal origin caused by viruses that normally only infect birds and, less commonly, pigs. It can be fatal to humans.

Earlier this week, four new human cases of H7N9 bird flu were confirmed in south China's Guangdong Province.

East China's Jiangxi Province also confirmed a human case of H10N8, a new strain of bird flu, on Wednesday.