0125 GMT February 23, 2020
Authorities discovered the virus in a sample of 120 chickens imported from the nearby Chinese city of Huizhou and killed nearly 19,000 birds, including 11,800 chickens.
"The rapid testing showed...that this batch of chickens carries the H7N9 virus," Hong Kong Government's Health Minister Ko Wing-man said Wednesday.
Televised images depicted authorities beginning the slaughter Wednesday morning with health officials dropping chickens into plastic bins.
The bins were then blown up with carbon dioxide to slaughter the birds, a spokeswoman for the city's agriculture department said, adding that the carcasses were disposed of after the operation.
The import of poultry from the mainland has been barred for three weeks.
The cull in Hong Kong comes days after a woman was hospitalized with the disease.
A 68-year-old woman has been receiving treatment for the virus since December 25 when she was returning to Hong Kong from the southern Chinese city of Shenzhen.
Following the new case - the city's first since early 2014 - Hong Kong raised alert levels in hospitals, with extra precautions taken from Sunday.
Hong Kong slaughtered 20,000 chickens in January after the virus was found in poultry imported from the neighboring southern Chinese province of Guangdong.
Mass poultry culls have been also conducted in other Asian countries.
South Korea has killed millions of chickens this year in a bid to end the spread of bird flu. Japan this week culled 37,000 chickens after the third bird flu outbreak there in less than a month.