The Centre for Health Protection's Acting Controller Dr Leung Ting-hung expects the preliminary test results for the samples taken from the Yuen Long chicken farm -  where a recent avian flu outbreak has occurred - will be ready in a week.

On a radio programme today, Dr Leung said government and Mainland laboratories will check whether there is any virus mutation, adding the Government will enhance the vaccines' effectiveness when the situation warrants it.

He noted the six Yuen Long farm workers who had direct contact with the dead chickens, as well as those involved in the recent chicken-culling operation, are under close medical surveillance. All of them are healthy.

Assistant Director of Agriculture, Fisheries & Conservation (Inspection & Quarantine) Dr Thomas Sit said the department is investigating the outbreak, and has collected samples from the farm for testing.

While it will seek more information from some complainants claiming smuggled eggs was the cause, Dr Sit said should this be true, small chickens should have died instead of the older 'sentry chickens' as happened this time.

Noting the Government has stringent controls on egg flows in Hong Kong, including random inspections, he believed chicken farmers would not take the risk of smuggling eggs.

Dr Sit added the department will conduct a thorough check on all farms during the 21-day live chicken ban.