Tung Wah Group of Hospitals Wong Tai Sin Hospital reported three deaths as its influenza A cluster grew by 14 cases to a cumulative 24 on 14 September.
The deaths involved three male patients aged between 81 and 95. The hospital said all three had serious underlying illnesses.
The newly identified cases included six male patients aged 63 to 95 in the chest medicine ward and seven female patients aged 55 to 85 in a convalescent ward. One staff member also tested positive and was on leave.
The other 10 newly reported patients were receiving isolation treatment and were in stable condition, according to the hospital.
The hospital said it had thoroughly cleaned and disinfected the ward.