SYDNEY: Australia said it would review some of its border reopening plans this week after reporting its first cases of the Omicron coronavirus variant, but urged calm until the seriousness of the strain was determined.

Four people who arrived in Sydney from southern Africa on Sunday tested positive for the newly identified variant as officials ordered 14-day quarantine for citizens returning from nine African countries. Another person who arrived in the Northern Territory from South Africa tested positive.

Prime Minister Scott Morrison said on Monday Australia would review plans to reopen borders to skilled migrants and students from Dec. 1. But he said it was too early to reinstate two-week mandatory hotel quarantine for all foreign travellers and urged patience since data had not yet determined the severity, transmissibility and vaccine resistance of the Omicron strain.

"We just take this one step at a time, get the best information, make calm, sensible decisions," Morrison told Nine News.

Omicron, dubbed a "variant of concern" by the World Health Organization, is potentially more contagious than previous variants. But health authorities do not know yet if it will cause more or less severe COVID-19 compared to other strains.

Morrison said the national security committee would meet later on Monday to assess border reopening relaxations due from Dec. 1, while federal, state and territory leaders would meet on Tuesday.

Australian employers have been calling for a resumption of arrivals by students and skilled migrants due to a labour shortage from the information technology sector to kitchen staff in restaurants.

The return of foreign students, who are worth about A$35 billion ($25 billion) a year to the Australian economy, will be a major boost for the education sector.

Federal Health Minister Greg Hunt said he asked the country's immunisation advisory group to review the timeframe for COVID-19 booster shots, in light of the new strain. About 87% of Australia's population aged over 16 is fully vaccinated, above the rates seen in the United States, Britain and much of Western Europe.

The variant emerged as Sydney and Melbourne, Australia's largest cities, began to allow vaccinated citizens entry from overseas without quarantine from Nov. 1, having shut their borders for more than 18 months.

Both cities have tightened their travel rules with all international travellers ordered to quarantine for 72 hours. Other states have not opened their borders to foreign travellers yet due to varying vaccination rates.

Australia has so far recorded about 209,000 coronavirus cases and 1,997 deaths since the pandemic began.

Neighbouring New Zealand, which has closed its borders since early 2020, said it would go ahead with a planned relaxation of domestic movement restrictions from this week, regardless of Omicron.