The Centre for Health Protection has warned that schools may be shut if a student were to die of flu.
Flu has claimed nine lives in Hong Kong so far this year. The current strains of flu include H1N1, also known as swine flu.
A number of dead birds found on Lantau tested positive for the H5N1 'bird flu' virus, but there have been no cases of human infection in the city.
A seven-year-old girl who had been ill died last week after being admitted to hospital. Tests will tell what strain of the virus she had.
Centre controller Dr Thomas Tsang Ho-fai said there may be small outbreaks in schools as students return from their holidays and are brought together in confined spaces.
He said that if a student were to die of flu, their school could be closed for a week. If the situation became more serious, classes would be suspended indefinitely.
Nine people in Hong Kong died of flu between January 24 and yesterday. Tsang warned that the peak flu infection period in the city would last until around late March.
Tsang stressed that if students had symptoms of flu, such as fever or difficulty breathing, they should consult a doctor immediately and stay home.
The centre urged people in the high-risk group to be vaccinated as soon as possible. These include young children, the elderly, the chronically ill and pregnant women. More than 362,000 people have been vaccinated for flu under a government-subsidised scheme. Tsang warned earlier that the public should not underestimate flu, as it could be fatal. People should maintain good personal hygiene and wash their hands frequently. Only the use of soap, and taking time to wash hands properly, will remove germs.
They should also exercise regularly and get plenty of rest to reduce stress. Smoking should be avoided as it will weaken resistance against flu and other diseases, the centre urged.
Secretary for Food and Health, Dr York Chow Yat-ngok, said last month that more people would get flu this year and more of them would develop serious complications.
He warned that this season's flu would be particularly serious. This is because people who had built up any immunity during the last big flu outbreak would most likely have lost it by now.