Hanoi authorities announced an outbreak of bird flu last week, one week after it was known that thousands of culled ducks had tested positive for the H5N1 virus.
Nearly 2,600 ducks from a local pond were culled in Dong Tien Hamlet of Phuong Duc Commune in Hanoi's outlying Phu Xuyen District on February 17, the news website VietNamNet reported Monday.
Five days later, the Central Animal Health Diagnosis Center at Vietnam's Health Ministry confirmed that the fowl had tested positive for bird flu.
But the hamlet only released the information on March 1, making it the first reported outbreak bird flu in the capital city this year.
The commune has nearly 25,000 ducks being raised by 18 families.
Phung Van Tao, head of the district animal health center, said the infected flocks were between 21 and 42 days old and had not been vaccinated against bird flu.
Tao told VietNamNet the ducks were not raised in caged enclosures.
Bird flu virus has infected three people in Vietnam this year, including two fatal cases in the Mekong Delta in January and one from Binh Duong Province who was released from the hospital Tuesday.
It has infected flocks in 12 provinces in northern and central Vietnam.
Vietnam health authorities have warned that a crisis may be underway, as the country is not equipped with a proper vaccines to combat the spread of the virus, which has mutated and is now resistant to previously effective vaccines.