NEW DELHI, July 25 (Reuters) - Authorities were testing chickens at a small poultry farm in India´s remote northeast for bird flu after a number of birds died suddenly, a senior official said on Wednesday.

The "unusual mortality" this month left 133 chickens dead out of 144 at the farm in Manipur state, said Upma Chawdhry, Joint Secretary of the Animal Husbandry Department.

"The mortality was sudden, just in the space of a few days," Chawdhry said.

She added 20 people living on the farm were taking Tamiflu, the most popular drug for treating and preventing bird flu, as well as six veterinary workers as a "matter of abundant precaution".

The government expects the results from tests on the blood and tissue samples of the birds this week, including for the highly pathogenic H5N1 virus. Chawdhry said the remaining chickens at the farm had been killed and the area sanitised.

Manipur, a remote state that is racked by separatist violence, borders Myanmar, which has fought outbreaks of bird flu among poultry this year.

India has reported no outbreak of bird flu in its multi-billion dollar poultry industry or among backyard poultry this year, despite nearly a dozen alerts.

It declared itself bird flu free last August after two major outbreaks among chickens in the west of the country in 2006.

India has asked it border guards to prevent people from bringing in poultry illegally from Bangladesh, China and Myanmar, Chawdhry said.

China and Bangladesh -- which neighbour India´s northeast -- have reported bird flu among chickens this year, with China also reporting human cases and deaths due to the H5N1 strain.

Globally, the H5N1 virus has killed nearly 200 people out of more than 300 known cases, according to the World Health Organisation, while hundreds of millions of birds have died or been slaughtered.