All poultry at the retail level will be culled as the H5N1 bird flu virus has been found in three more markets, Director of Agriculture, Fisheries & Conservation Cheung Siu-hing says.

The order was given after positive samples were taken from Luen Wo Hui, Ap Lei Chau and Tuen Mun Yan Oi Markets. All markets and retail food shops selling live poultry have been declared an infected area.

Noting public health is the Government's priority, Ms Cheung said more samples will be collected for tests and the infection source will be traced.

Deputy Director of Food & Environmental Hygiene Alice Lau said department staff have cordoned off all 260 poultry stalls in 64 markets and 209 retail food shops and started culling poultry. Disinfection work will also be conducted.

Secretary for Food & Health Dr York Chow said live poultry imports from the Mainland will be suspended for 21 days and local farms will stop dispatching poultry to the market.

"We will discuss with traders on how to enhance preventive management at retail level. Our primary concern is to safeguard public health. If the improvement measures cannot be implemented at the retail level, we do not rule out extending the 21-day suspension of live chicken imports," he said.

The discovery of avian influenza virus in a number of markets showed the current monitoring system is effective, Dr Chow added.

"But this also shows there might be inadequacies in the preventive and control measures in retail markets. The Government needs to review the supply chain of chickens, including the bio-security measures in farms and the licensing conditions of retail markets."

Assistant Director of Agriculture, Fisheries & Conservation Dr Thomas Sit said all 120 samples collected from Cheung Sha Wan Temporary Wholesale Poultry Market and 150 samples from 50 poultry farms in Hong Kong have tested negative for the virus.

As local farms have adopted stringent biosecurity measures and operate in an enclosed environment, they are relatively safe and there is no need to cull all chickens in local farms.

Assistant Commissioner of Customs & Excise Tam Yiu-keung said there is no evidence of poultry smuggling activities at Po On Road Market, the first local market declared an infected area. Urging the trade and public to report suspicious cases, Mr Tam said the department will enhance its investigation.

Centre for Health Protection Controller Dr Thomas Tsang said although no human avian flu cases have been reported so far it has enhanced prevention and surveillance work.

The health of poultry staff will be monitored, he said, adding Po On Road Market workers being kept under surveillance since Saturday have not developed symptoms.