As many as 100 chickens were found dead at a poultry farm in Vehloli village of Shahapur tehsil in Thane district, said Thane District Magistrate and Collector Rajesh J Narvekar on Friday.
Considering the bird flu threat, the samples have been sent to a lab in Pune.
He further said that around 25,000 birds falling in a kilometre radius of the affected poultry farm will be killed within the next few days.
The district animal husbandry department has been ordered to take measures to control the infection.
Avian influenza, commonly called bird flu, is an infectious viral disease of birds (especially wild water fowl such as ducks and geese). Wild birds can carry the virus without showing symptoms of it and transmit it to poultry through their feathers or feces.