Bangladesh's livestock authorities are slaughtering around 150,000 chickens at a giant poultry farm near Dhaka after the worst outbreak of avian flu in five years, officials said Wednesday.

The deadly H5N1 strain of flu was detected at Bay Agro farm at Gazipur, 40 kilometres (25 miles) north of Dhaka, on Monday after dozens of chickens died, prompting the company to send samples to a laboratory for tests.

"There are about 150,000 chickens at the farm. We have already killed and destroyed 120,000 chickens and we will kill the rest today," livestock department director Mosaddeq Hossain told AFP, adding it was the worst bird flu outbreak in five years.

Bangladesh was hit by bird flu in February 2007, when over one million birds were slaughtered on thousands of farms. Since then the flu has entrenched in the country, seriously ravaging one of the world's largest poultry industries.

The last major outbreak was in March 2010 when at least 117,000 chickens and 200,000 eggs were destroyed at a farm in northern Bangladesh.

The latest outbreak is the 23rd to be recorded this year. Even before the new mass slaughter, a total of 107,252 chickens had been destroyed in 22 farms, said Ataur Rahman, a livestock control room official.

The country has also reported six confirmed human cases of bird flu since May 2008, but the government's health department said all have recovered.