Australia has shut its borders to nine southern African countries and suspended all flights from the region amid concerns about the Omicron variant of COVID-19.
Health Minister Greg Hunt says Australia is in a vastly different position to other countries due to high vaccination rates, but precautionary measures are needed against the new strain.
Mr Hunt says all flights have been halted from South Africa, Namibia, Zimbabwe, Botswana, Lesotho, Eswatini, the Seychelles, Malawi, and Mozambique for two weeks.
Australian citizens or their dependents who have been been in those countries in the past 14 days must go into mandatory quarantine on arrival, while non-citizens who have been in southern Africa will be banned from entering Australia.
Anyone who has already arrived in Australia from any of those nine countries must go into immediate self-isolation and get tested.
"There are no known cases of the Omicron variant in Australia," Mr Hunt told reporters on Saturday.
"We've taken precautious action in the past, we've taken early action in the past. We are doing that again."
The number of people who have arrived from southern African since November 1 is thought to be less than 100.
One of those travellers has tested positive in the Howard Springs quarantine camp the Northern Territory.
Authorities are still waiting for genomic sequencing to reveal which strain it is.
The new variant, named Omicron by the World Health Organisation on Saturday morning AEDT, first emerged in Botswana and has been detected in South Africa, Hong Kong, Israel and Belgium.
It has double the number of mutations as the Delta variant that sparked a third wave of outbreaks and lockdowns in Australia this year.
Chief Medical Officer Paul Kelly said Omicron was spreading quickly, but it wasn't clear that it caused more severe symptoms than existing strains or if it could evade vaccine immunity.
Concern over the new variant prompted a wave of changes to state border regimes on Saturday evening.
In NSW, arrivals who've been overseas anywhere in the past 14 days must isolate at home for 72 hours pending further advice.
The isolation requirement is two weeks for flight crews, unless they leave the country first.
Anyone already in the state's who been in one of the nine African countries in the past 14 days must isolate for two weeks, be tested, and contact NSW Health.
Western Australia will immediately tighten its border with South Australia, with arrivals from that state required to isolate at home for 14 days and be fully vaccinated.
Premier Mark McGowan said the uncertainty around the new variant meant his state needed to have protections in place for states with relaxed international borders.
WA already has strict border controls in place for NSW, Victoria and the ACT.
Mr McGowan said he wouldn't yet be changing his plan to open interstate borders when his state's vaccination levels are higher.
South Australia in turn will force international arrivals into two weeks of quarantine, four days after allowing seven-day quarantine for Australian citizens.
Interstate travellers must now provide evidence of a negative test taken before their arrival.
Tasmania will ban travellers from southern Africa until they have completed 14 days of supervised quarantine, and the required testing, in the mainland state where they arrived.
It comes as Victoria recorded another 1252 cases and five deaths, and thousands of people protested vaccine mandates in Melbourne for a third consecutive weekend.
Saturday's demonstration came a day after a mandate came into effect for all authorised workers, including AFL stars, athletes, first responders, hospitality and retail workers, personal trainers, and manufacturing and mining workers.
Mandates earlier came into effect for workers in construction, freight, health care, aged care and education.
NSW recorded another 235 new cases were reported on Saturday.
Australia has fully vaccinated 86.6 per cent of residents over 16, and 92.2 per cent have had one dose.
About 1.5 per cent have had a booster shot.
Australian Associated Press