HANOI (Reuters) – Vietnam has so far this year culled tens of thousands of birds to contain an outbreak of highly pathogenic H5N6 bird flu detected at several farms in its northern provinces, an agriculture ministry official and state media said on Monday.

The authorities have culled the birds, mostly chicken and ducks, at farms in Nghe An, Thanh Hoa and Quang Ninh provinces, said the official, who declined to be named because he was not authorised to speak to the media.

Thanh Hoa province, 170 km (105 miles) south of Hanoi, has culled 23,000 birds at 10 household farms after they tested positive to the virus, Thanh Hoa newspaper reported on Monday.

“We are concerned that the virus may spread further, and are trying our best to stop the outbreak,” the official said. Apart from culling the birds, the authorities have also disinfected the farms and put a ban on poultry transport from the infected zones, the official said.

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H5N6 virus has also been detected in poultry at a farm outside Hanoi, prompting the culling of more than 2,300 birds there, Kinh Te Do Thi newspaper reported.

Vietnam has a poultry herd of 460 million, and small-sized bird flu outbreaks have not been uncommon in the country during the past five years, the official said.

(Reporting by Khanh Vu; Editing by Alex Richardson)