Veterinary workers began killing thousands of chickens in eastern India on Wednesday following what the World Health Organisation (WHO) said was the worst outbreak of bird flu in the country.
Officials said it could take up to a week to cull about 350,000 birds in three districts of West Bengal.
The WHO's India office said the fourth bird flu outbreak in India since 2006 presented its toughest challenge yet.
West Bengal has sealed a stretch of its border with Bangladesh, which has been fighting to contain the spread of bird flu since March last year. Bird flu has spread to another district in Bangladesh, forcing authorities to cull more than 1,500 birds, officials said on Wednesday.