Two girls, aged one and four, in the region have been diagnosed with the second strain - which has been identified by experts from the United States Centers for Disease Control as H9N2 - but have recovered. Meanwhile, the authorities on the Chinese mainland have confirmed that five cases of it were identified in the southern provinces last year.
Like the original virus - classified as H5N1- the latest flu spreads from poultry to people, although the method of transmission is not clear. After the earlier outbreak, a much stricter hygiene regime for poultry was introduced. However, two weeks ago a sub-strain of H5N1 was found in a consignment of live ducks and geese at a market.
Yesterday, Stephen Lam, a government spokesman, admitted that there was no way to prevent the spread of bird flu but said officials were urgently looking into the source of the virus, its mode of transmission and what new measures could be taken against it.
Hong Kong has a record of developing such diseases. The bird flu, identified in 1997, followed a particularly virulent flu virus in 1968, which caused the deaths of 46,500 people worldwide.