The age threshold for COVID vaccinations in Hong Kong will likely be lowered to 16 by next week, the city's civil service secretary announced Tuesday as officials scramble to prevent dose wastage.

"We want everyone to use our existing vaccine supplies, so the next batch can come when they are used up," secretary for the civil service Patrick Nip Tak-kuen said during a radio program Tuesday.

Nip oversees Hong Kong's vaccination program, which is aiming to have 70% of city residents inoculated to achieve herd immunity.

Last week, authorities lowered the threshold to 30. This led to a massive wave of vaccine bookings as people moved fast to secure doses of the German-made Pfizer BioNTech jab.

Pfizer vaccine doses are particularly susceptible to environmental factors and must be stored at -70 degrees Celsius or risk spoiling.

To ensure no doses go to waste, authorities are looking at offering more incentives to encourage sceptical Hong Kongers to take either the Sinovac or Pfizer vaccine, according to city chief executive Carrie Lam.

"I will personally look into this matter," she said Tuesday.

Just over 5% of Hong Kong's 7.5 million residents have received their first dose of the vaccine so far.

Thanks to stringent social distancing and quarantining measures, there have been just 11,397 cases in the city to date, including 203 deaths.