HONG KONG - Hong Kong decided on Monday to tighten health quarantine arrangements on inbound travelers from 16 countries to fend off the more infectious Delta coronavirus variant.

Effective from 12:00 am on Friday, travelers from 15 countries, including the United States, France and Spain, will be required to be fully vaccinated and undergo a 21-day quarantine upon arrival, according to a statement of the Hong Kong Special Administrative Region government.

Those countries will be upgraded from the medium-risk category to high risk.

Australia will be moved from low risk to medium risk so that non-vaccinated visitors from the country have to undergo quarantine for 21 days and those fully vaccinated will be quarantined for 14 days, or seven days with a positive antibody test.

The decision to tighten quarantine arrangements was to strengthen the local barrier against the importation of the virus in view of the recent surge of infections with the Delta variant overseas, the government spokesperson said.

Meanwhile, Hong Kong reported three new imported COVID-19 cases on Monday, taking the total tally to 12,036. In the past 14 days, a total of 46 cases have been reported, with one untraceable local infection and the rest imported.

Hong Kong's vaccinated population continues to grow. Around 3.73 million people, or 54.8 percent of the eligible population, have taken at least one shot of the vaccine, while around 2.91 million are fully vaccinated.