The World Health Organisation Thursday warned that an outbreak of bird flu in eastern India was far more serious than two previous outbreaks, as officials reported more poultry deaths.
"More serious risk factors are associated with this current outbreak than previously encountered, including that the affected areas are more widespread and because of proximity to extended border areas," the organisation said.
The warning came as Anisur Rahaman, animal resources minister in West Bengal state, where the outbreak was reported, said the virus had spread to settlements around the village where the first poultry deaths came to light.
"Reports have reached (us) that hens have started dropping dead in several villages surrounding Margram. We are worried over the situation. We have sought more help from the federal government," Rahaman told AFP.
Health officials are engaged in culling 400,000 birds in several districts of India's heavily populated West Bengal state bordering Bangladesh, which is also struggling with the virus.
The slaughter started after India's agriculture ministry confirmed that the death of an estimated 35,000 birds in West Bengal was due to the deadly H5N1 strain.
About 8,000 birds were killed Wednesday, the first day of the cull, Rahaman said, adding officials were facing resistance from bird owners.
"We have asked health workers to step up culling.... The government has a target to cull 350,000 chickens in the next 10 days," he added.
Meanwhile, Pradip Roy, a railway employee working at Birbhum station near Margram said villagers were crowding local markets "to buy chickens at low prices."
"A good number of chickens are also being smuggled out," Roy added.
In New Delhi, officials said advisories had been sent to states neighbouring West Bengal in a bid to contain any possible spread. Flights originating from Kolkata had taken chicken off their menus.
An isolation centre has been opened in a hospital near the affected area and 300 health workers have been sent with medicines and protective gear, Rahaman said.
The outbreak is the third in India, home to 1.1 billion people, since 2006.
Humans are typically infected by coming into direct contact with infected poultry, but experts fear the deadly virus may mutate into a form easily transmissible between humans.
Wild migratory birds have been blamed for the global spread of the disease, which has killed more than 200 people worldwide since 2003.