HONG KONG began a mass cull of 20,000 chickens yesterday after the deadly H7N9 bird-flu virus was discovered in poultry imported from mainland China, authorities said. Fears over avian bird flu have grown following the deaths oftwo men in Hong Kong since December. Both had recently returned from mainland China. Officials wearing masks and protective suits piled dead chickens into black plstic bags at the wholesale market in Hong Kong where the virus was discovered on Monday, television footage showed. "It [the culling] has started, an Agriculture, Fisheries and Conservation Department spkesman told AFP. The chickens would be given a "chemical treatment" to kill them, after which they would be sent to landfill, the spokesman said. The positive H7N9 reading was discovered in chckensat Cheung Sha Wan market on Monday, which will be closed for 21 days for disinfecting. Cheung Sha Wan is the only wholesale poultry market in Hong Kong and is a holding centre for chickens awaiting test results. Chickens supply to markets from local Hong Kong farms was also suspended.