KOLKATA, India (AFP) - Nearly 20,000 chickens have died in eastern India in the past week, triggering fears of an outbreak of bird flu, officials said.

Samples from dead birds have been sent to a laboratory in central India to determine if the deaths were due to the H5N1 virus.

"The dead birds showed the flu symptoms," said S.K Bhowmic, the chief health officer of the affected district in eastern West Bengal state.

The poultry deaths were reported from farms in the state's Morgram village, about 125 kilometers (75 miles) from state capital Kolkata.

Preliminary tests suggest bird flu to be the cause of the deadly infection, state animal resources development minister Anisur Rehman said. A final report was expected later Monday.

Locals have been asked not to sell chickens, and security along India's border with Bangladesh had been stepped up to stop imports from the neighbouring country, which is also hit by bird flu, the minister said.

India reported an outbreak of bird flu among poultry in July, the first since it declared itself free of the deadly disease in August 2006.

Humans are typically infected with bird flu by coming into direct contact with infected poultry, but experts fear the H5N1 virus may mutate into a form easily transmissible between humans.

The infection has killed more than 200 people worldwide since 2003.