Authorities in Assam have culled some 40,000 poultry of an estimated 60,000 birds ordered to be killed after an outbreak of the deadly bird flu virus in the region, officials Monday said. Culling operations are on in the district of Kamrup since Friday and so far about 40,000 chickens and ducks were killed, said Manoranjan Choudhury, deputy director of the Assam Veterinary department. The culling is being carried out in about 48 villages within a five kilometre radius of village Thakurchuba in Kamrup district, about 40 km west of Assam's main city of Guwahati. The poultry targeted includes ducks and chickens. Some 22 Rapid Response Teams are engaged with the operation expected to be completed in the next two to three days. The Indian health ministry last week confirmed outbreak of bird flu after laboratory tests found strains of the deadly H5N1 avian influenza. More than 300 birds died in the past one week in the area. Assam's veterinary and animal husbandry department has sounded an alert and maintaining strict surveillance on farms in the state with veterinarians carrying out checks on all poultry. A central health ministry team is also assisting the local authorities in the culling operations. The World Health Organisation fears that the H5N1 strain could mutate into a form easily transmitted between humans and spark a deadly pandemic. Sale and purchase of poultry in the area was banned.