Fresh calls have been made for Hong Kong to find the latest source of bird flu in the city, after disclosure of a fatal H5N1 outbreak in Guangdong ducks. Hong Kong was told by the Ministry of Agriculture yesterday that the outbreak occurred in Yashan village in the Xinhui district of Jiangmen on June 10, and that nearly 4,000 of the 21,000 ducks on the farm had died by Friday. Hong Kong officials detected H5N1-positive chicken droppings at Po On Road market in Sham Shui Po on June 7. Last Wednesday, three more markets were found to be infected, triggering closure of all wet markets and the culling of about 5,000 birds. A 21-day ban was placed on imports of mainland poultry. Last night, in response to the Guangdong announcement, the Food and Health Bureau imposed a 21-day ban on imports of poultry and pet birds from farms within a 13km radius of the infected duck farm. Only one farm in that area, 7km from the infected farm, is known to be licensed to supply poultry to Hong Kong. The legislator for the medical sector, Kwok Ka-ki, said another outbreak of H5N1 on the mainland made it even more critical for Hong Kong to find the source of the virus. 'The government should not only be concerned about that one farm, but should check with Guangdong authorities if any other farms were involved. Is it the case that the source of H5N1 was the southern part of [Guangdong] province?' Chicken traders yesterday suggested setting up a system of tags that could be laser-scanned for both local and mainland-imported chickens, in the hope the government would withdraw the proposed ban on stocking live chickens overnight at markets to combat bird flu. The tags would be attached to all chickens from local and mainland farms, to allow tracking of live poultry and to fight smuggling. A Hong Kong factory owner based in Yashan said yesterday that most of the duck farmers in the village were from Zhejiang province , rather than locals, and dozens of them bred fish and ducks together. 'I've heard of massive deaths of ducks for several days. Initially, farmers were reluctant to report the case to the local agriculture and fisheries department but, when the virus spread, they could no longer cover it up any more and the officials came,' the factory owner said.