Hong Kong on Sunday reported 65 newly confirmed cases of swine flu, bringing to 320 the total number of infections in the southern Chinese city.
The new cases involved 32 male and 33 female patients aged between seven and 57 years old, the Department of Health said, without commenting on their condition.
The department said four secondary schools, attended by students among Sunday's confirmed cases, had also been advised to close for 14 days.
Earlier this month, authorities ordered all primary schools in the city to be closed for two weeks after the first cluster of local swine flu cases was found.
When Hong Kong discovered its first case, in early May, health authorities quarantined around 300 guests and staff at a hotel where the carrier, a Mexican, had briefly stayed.
Hong Kong is particularly nervous about infectious diseases following the outbreak of the SARS virus in 2003, which killed 300 people here and a further 500 around the world.
Swine flu, or influenza A(H1N1), has infected more than 44,000 people around the world in 95 countries and territories, causing 180 deaths since late March, according to the latest World Health Organization data.