Australian states and territories are reimposing border rules in response to the new Omicron variant of COVID-19, which has now been detected in a growing number of countries across the world.
On Saturday, Australia tightened its international border to travellers from nine African countries where the new variant of concern has been found.
People arriving from South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia, Eswatini, Malawi, and the Seychelles into any Australian state or territory must undergo 14 days' quarantine.
In a dramatic change to border rules, New South Wales and Victoria later announced all vaccinated travellers from all other countries would be required to isolate for 72 hours on arrival into the state.
The ACT has taken similar measures, with all recent international arrivals from all other countries required to quarantine until November 30.
It comes less than a month after the NSW completely removed all quarantine requirements for fully vaccinated international arrivals.
Victoria and the ACT followed suit, effectively opening the international border to half of the country from the start of November.
But now fully vaccinated arrivals into both NSW and Victoria must self-isolate for 72 hours after arrival.
The states have also imposed new rules on international flight crews, who need to isolate for 14 days or until they leave on another flight — bringing the rules for vaccinated crew into line with unvaccinated workers.
No confirmed cases of the Omicron variant have been reported in Australia to date.
Scientists are still working to understand the new strain, how it spreads and the effectiveness of vaccines against the variant.
NSW Premier Dominic Perrottet said the reintroduction of quarantine rules was to "put community safety first by taking these precautionary but important steps until more information becomes available".
Victoria's Acting Chief Health Officer Deborah Freidman said the changes were "safe and proportionate" and were designed to protect Victorians while still letting overseas arrivals into the state.
The measures will be in place for at least three days in NSW and Victoria.
About 100 people who had flown from the nine countries into the states and territories where quarantine was not compulsory were now required to do so.
Changes in South Australia and Western Australia
South Australia announced a tightening of its border rules, less than a week after reopening to the rest of the country.
Travellers from "low-risk" regions like Sydney and Melbourne will have to show evidence of a negative test result from within 72 hours before arriving in SA.
Police say there is no provision to be tested on arrival.
Cross-border community members will need to quarantine until a negative test result on arrival if travelling with children under 12.
International arrivals from any country will have to quarantine for 14 days, rather than just seven, due to concern over the Omicron variant.
If an Australian jurisdiction is classed "high risk", the same 14-day quarantine rule will apply.
"With the emergence of the Omicron Variant all international travellers and people arriving from High Risk locations from within Australia arriving in South Australia or International travellers transiting through another port directly to South Australia must now undertake 14 days quarantine," South Australia Police said.
SA has this week recorded its first cases of local transmission in months, after opening its borders to the rest of the country.
Western Australia tightened its border with SA on Saturday night in light of the new infections, citing concerns about the Omicron variant.
Other states and territories are mulling how to respond to the new variant, which has prompted tightened border rules in dozens of countries since it was officially called a variant of concern.
