The outbreak was reported from West Bengal's Murshidabad district where 900 chickens and ducks died over the last two weeks, officials said.

In January, the H5N1 virus had hit 13 of the state's 19 districts, including Murshidabad, bringing down poultry sales by more than 70 per cent in the state, but it had a limited impact in rest of the country.

Authorities had then culled more than 3.4 million birds in the state after the World Health Organisation (WHO) described the outbreak as the worst-ever in India.

There were no reported human cases of the bird flu. Experts fear the H5N1 strain could one day mutate into a form easily transmitted from person to person, leading to a pandemic that could kill millions worldwide.

Officials in eastern India say bird flu among poultry could spread to new areas.

'We do not know how many chickens and ducks escaped culling during the earlier exercise, but we are now trying our best to find them,' Anisur Rahaman, the state's animal resources minister told Reuters from the state capital, Kolkata.

Bird deaths were also reported from neighbouring Birbhum district, the epicentre of the original outbreak in January.

'We don't think it is bird flu, but we are collecting samples from Birbhum for testing,' Mr Rahaman said.

Smuggled poultry
The minister said smuggled poultry from bird-flu hit Bangladesh could have triggered the latest outbreak.

Bird flu spread to another district in Bangladesh last week, affecting 47 out of 64 districts in the country, struggling to contain the outbreak.

In India's bordering district of Murshidabad, over 350 veterinary workers were catching chickens and ducks on Monday from homes and slaughtering them by wringing their necks, officials and witnesses said.

At least 50,000 chickens and ducks will be slaughtered in the next few days to contain the latest outbreak, a senior district official said.

Earlier culling efforts had been hampered when villagers refused to hand over their chickens and even let them loose to avoid getting caught.

'We are determined to cull all backyard poultry in a 5km radius and ensure a better job this time,' Subir Bhadra, a senior official said.

While India has so far not reported any human infection, but health workers were moving in villages to look for people with flu-like symptoms.

'We are well-prepared and a strict surveillance is in place now,' Mr Rahaman said.

The WHO said recently the virus was firmly entrenched in Asia and a pandemic among humans was possible. -- REUTERS