The move comes after two travellers from South Africa tested positive fro Covid-19 after landing in Sydney on a Qatar Airways flight from Doha on Saturday night.
Urgent testing is underway to determine if they are carrying the new variant of concern.
The infected passengers have begun 14 days of quarantine at a special health facility.
NSW Health said other passengers on the flight may be considered close contacts and will be requested to get tested immediately.
It comes after a traveller from South Africa tested positive for Covid-19 in the Northern Territory on Friday. Testing is also underway to see if they carry Omicron.
Global alarm triggers new travel rules
NSW, Victoria, SA and the ACT have introduced new rules for all international travellers in a bid to contain the spread of Omicron.
NSW and Victoria have both introduced 72-hour isolation requirements for all vaccinated international arrivals, regardless of their departure destination.
In SA, all international travellers from high-risk locations in Australia will once again be required to quarantine for 14 days. It’s unclear whether hotel or home quarantine is required at this stage.
The ACT government has also announced that any fully vaccinated overseas travellers arriving as of midnight from countries other than those six Southern African nations must quarantine until 11.59pm on Tuesday, November 30.
Western Australia currently requires international travellers and those coming from South Australia to quarantine for 14 days.
International travellers entering Queensland must quarantine for 14 days, while full vaccinated domestic and international arrivals into the NT from a Covid red zone may be allowed to undertake seven days of home quarantine.
NSW Premier: International borders will remain open
NSW Premier Dominic Perrottet said during a press conference on Sunday that the new travel restrictions are a reminder that the pandemic is not over, and described his approach as precautionary.
However, he cautioned that it must be expected that the variant will spread throughout the world.
"We need to learn to live alongside the virus. We need to learn to live alongside the variants of the virus," he said.
Mr Perrottet insisted the NSW international and state borders would remain open.
"We can't be a hermit kingdom on the other side of the world," he said.
"There's only so much governments can do. The best thing we can do as a people is to get vaccinated, get a booster shot, and that will keep you and your family safe."
The changes come after Australia shut its borders to nine southern African countries as health officials scramble to learn more about the emerging threat.
The World Health organisation said the new variant of concern may spread more quickly than other strains and poses a much higher risk of reinfection because it has double the number of mutations as the deadly Delta variant.
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