More than 40,000 birds were destroyed at six farms. Officials earlier said only one farm at Savar, 40 kilometres (25 miles) west of the capital, had been was affected.
"Six farms with 42,400 chickens were infected by bird flu," interim government cabinet member Sajjadul Karim told reporters on Friday, adding that all the birds had now been killed.
Officials confirmed Bangladesh's first case of bird flu late Thursday after samples from one of the farms were sent to the National Institute of Animal Health in Bangkok, which confirmed the presence of the deadly H5N1 strain of the virus.
The caretaker government has agreed a string of measures to prevent the spread of the disease in the densely-populated South Asian country of 144 million people.
The virulent H5N1 virus has killed at least 169 people since late 2003, most of them in Asia, according to the World Health Organisation.
Scientists fear the virus could mutate into a form easily spread among humans, leading to a global pandemic with the potential to kill millions.
Bangladesh is home to hundreds of thousands of poultry farms which employ more than a million people.
The country had already banned imports of live birds from more than 50 countries including neighbouring India and Myanmar after outbreaks were detected there.