Two more patients have developed respiratory illness symptoms at the Caritas Medical Centre, bringing the total cases to 30. Among them, six have fever, while the condition of the patient in intensive care is improving.

The 29 others are in an isolated ward where infection-control measures have been tightened as the Green Alert infectious disease response is still in force.

Initial investigations have ruled out SARS or common influenza, but further tests are needed to establish the source and type of infection.

Secretary for Health, Welfare & Food Dr York Chow believes the virus, which is affecting children with weaker immunity, is not necessarily a new virus.

The Centre for Health Protection, the Chinese University and the University of Hong Kong are tracing the source of infection.

Dr Chow reminded people to take precautionary measures to safeguard their health with the approach of winter, adding that people who develop respiratory illness symptoms should stay at home.