The outbreak was detected at two breeding households in Ngoc Xuan ward, Cao Bang city, in which 700 birds died and 2,004 others, including 1,974 ducks and 30 chickens were culled.
Right after the report on the outbreak, the provincial animal husbandry sub-department and local authorities have taken required measures.
The new incident brought the number of A/H5N1 outbreaks in the country to six and the A/H5N6 outbreak to two.
Affected localities include Cao Bang, Can Tho, Vinh Long, Dak Lak, Quang Ninh and Thua Thien-Hue.
The Animal Health Department said there are high risks of bird flu spread and required localities to proactively act and intensify the control of fowl smuggling to promptly detect any outbreaks.
It warned that though A/H7N9, A/H5N2, A/H5N8 strains are yet to be found, they are likely to enter the country via the transport and trade of smuggled poultry without origin, especially in northern localities.