Hong Kong has prohibited non-residents from entering the city from four African nations and wants to extend the prohibition to passengers who have visited Canada, Australia, Israel, and six European countries in the preceding 21 days because of worries about the new Omicron variant of COVID-19.

Omicron - initially identified in southern Africa and carrying a "very high" risk of infection surges -- has sparked alarm around the world, with border closures casting a pall over a fledgling economic recovery from the ongoing global health crisis.

The Hong Kong government said late Monday that non-residents from Angola, Ethiopia, Nigeria, and Zambia would be prohibited from entering the global financial hub as of Nov. 30.

The statement added that the most strict quarantine requirements will also apply to relevant inbound travelers from these countries.

Residents who have been vaccinated may return, but will be required to spend seven days at a government facility and another two weeks in a hotel at their own expense.

Moreover, non-residents who have visited Australia, Belgium, Austria, Canada, Denmark, the Czech Republic, Israel, Germany, or Italy within the last 21 days would be denied entry to the city beginning Dec. 2.

Residents returning from these countries who have been vaccinated will be required to stay in a hotel for three weeks.

Hong Kong, one of the few remaining areas in the world pursuing a COVID-19-free approach, previously barred non-residents from South Africa, Eswatini, Botswana, Malawi, Lesotho, Namibia, Mozambique, and Zimbabwe.

City officials have identified three individuals with the Omicron variant through compulsory testing while in quarantine, but there are no documented coronavirus cases in the general population.

Five passengers with Omicron have been vaccinated and placed in quarantine in Australia, health officials said, adding that they are all asymptomatic or have very mild symptoms.

Canberra postponed the reopening of the country's borders for international students and skilled migrants on Monday, less than 36 hours before they were scheduled to return.

"We are proceeding cautiously, but our overall assessment is that, while Omicron is an emerging variety, it is a controllable variant," Federal Health Minister Greg Hunt said during a Canberra press conference.

Growing optimism that the new strain of the virus will be milder than anticipated has helped restore some calm to markets this week, following a Friday crash that saw the value of global stocks plummet by almost $2 trillion.

Meanwhile, Hong Kong hopes to partially reopen the border with mainland China in the coming months, as China, like Hong Kong, has no tolerance for coronavirus outbreaks.