An outbreak of avian influenza on a Bulgarian farm with over 177,000 laying hens has forced authorities to begin slaughtering the remaining flock, the country's food safety agency said on Monday.

The outbreak in the town of Asenovgrad is the sixth industrial farm hit by the highly pathogenic avian influenza type A in southern Bulgaria since December, reported Reuters.

The risk to humans from the disease is considered to be low, but past outbreaks among farm birds have resulted in extensive slaughtering programmes to contain the spread.