Bookings for such people will open on November 23, although there must be a gap of at least six months between a person’s second and third dose of vaccine.
Until now, only priority groups and those over 60 have been eligible for a booster.
Officials say operations have been smooth and the programme can now include more people.
“After assessing the capacity and service demand of the community vaccination centres and hospital Covid-19 vaccination stations, we have decided to expand the arrangements to cover more eligible persons to enhance protection,” a government spokesman said.
People can choose to get the Sinovac or BioNTech vaccine for their third jab.
Hong Kong authorities reported four new imported Covid-19 cases on Thursday.