By Biswajyoti Das

GUWAHATI, India, July 27 (Reuters) - Veterinary workers in protective clothing broke the necks of thousands of chickens on Friday while medical staff checked people for flu symptoms to contain an outbreak of bird flu in poultry in India's northeast.

The outbreak of avian influenza in chickens this month on a small farm in the remote state of Manipur was the first in India this year, making it the 25th country to report the occurence of the H5N1 strain in 2007.

Over 9,000 chickens have been killed in and around Chingmeirong village on the outskirts of Imphal, the state capital, before being thrown into huge pits that were then covered with lime and salt and finally with soil.

Authorities plan to kill 150,000 birds by next week in a 5 km (3 miles) radius of the village.

Officials said there were no reported suspected human cases in the state, which borders Myanmar.

But they said they would continue to question thousands of people around the affected area on whether they were suffering from flu symptoms and had contact with poultry.

Volunteers distributed surgical masks on the streets of Imphal, while some kept watch on trucks and three-wheeler vans to stop smuggling of poultry from the affected area.

"One auto-van loaded with chickens on its way out of Imphal was caught by some residents and handed over to the police," said Ashok Meitei, a local businessman.

In some neighbourhoods near the affected farm where medical teams had not yet visited, anxious residents opened camps and asked those suffering from fever to report for checks.

Officials say the outbreak in Manipur seems isolated.

Imphal is about 1,700 km (1,000 miles) from New Delhi, and closer to Bangkok than to the Indian capital.

Since 2003, a total of 192 people have died out of 319 people infected by the virus across the globe, the World Health Organisation says.

H5N1 remains largely a bird virus but experts fear it might mutate into a form that easily passes between people, triggering a pandemic in which millions could die.

In Manipur, some poultry farmers had stopped feeding their birds.

"We are scared to go near them," said Rajiv Singh, a poultry farmer near Imphal. "I am waiting for the veterinarians to come and kill these chickens."

India's northeast, connected to the rest of the country by a tiny strip of land, neighbours Bangladesh, Myanmar and China, all of which have been hit by bird flu in poultry, with China reporting human cases and deaths as well.

Indian troops on the state's border with Myanmar have stepped up patrols to prevent poultry smuggling.

Last year, India faced two major outbreaks of the H5N1 strain in chickens in the west of the country, before declaring itself bird-flu free last August.

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