Australia will continue its path towards a Christmas reopening while health authorities gather more information about the new strain.
Chief Medical Officer Paul Kelly told the state and territory heads it would be up to two weeks before there was enough information to paint a clear picture about the variant's threat.
But he said there was no evidence vaccines were less effective.
, insisting the new COVID-19 strain would not put Australia back into lockdown.
"We're not going back to lockdowns, none of us want that," he said.
Increased fines in NSW
NSW has increased its fines to $5000 for those who fail to comply with quarantine or testing requirements, up from $1000. The fine for corporations breaching requirements has been doubled to $10,000.
Premier Dominic Perrottet says it's a necessary precaution while the world waits to find out more about the Omicron variant.
"We are well prepared here in NSW, but it is important we take the necessary steps to protect the community and adopt measures that will allow us to learn to live with COVID," he said.
All international travellers entering NSW and Victoria will need to isolate for 72 hours and take a COVID-19 test.
A second test must be taken on day six after arriving in NSW, and between days five and seven in Victoria even after leaving quarantine.
All travellers entering NSW from eight southern African nations, or nine in the case of Victoria, will need to quarantine for 14 days.
Visa holders, who were set to be allowed into Australia on 1 December, will now have to wait until 15 December to enter the country without an exemption.
The prime minister said a two-week pause on the next stage of Australia's reopening plan was sensible in order for health experts to assess the risk posed by the new variant.
Omicron had also delayed travel bubble arrangements for citizens from Japan and South Korea.
The Australian Technical Advisory Group on Immunisation is examining whether to recommend booster COVID-19 shots sooner in light of the variant.
They are currently recommended for six months after a second vaccine dose.
NSW records fifth Omicron case
A fully vaccinated woman aged in her 30s became the NSW's fifth confirmed Omicron case on Tuesday, and unlike the two cases confirmed on each of the previous two days, she had visited a number of shopping centres, supermarkets and fast food outlets on Friday and Saturday last week, after travelling from southern Africa.
The woman is now isolating at home on the Central Coast and will not be targeted by the change to penalties as she had not been required to isolate at the time she arrived.
The other four people NSW Health genomically confirmed have the Omicron variant were in special health accommodation since they arrived in Australia thanks to those changes, which didn't capture the woman who arrived on Thursday last week.
Two more people on her Thursday flight from Doha have since tested positive, and neither of them had been in southern Africa.
Urgent genomic testing is underway to see if they have the Omicron variant.
NSW Health Minister Brad Hazzard says those eligible for booster shots should now be booking in appointments to get the jab, calling boosters "our best defence against what can be a deadly virus".
He says the government is "taking this new variant very seriously" and people should think twice before skipping isolation requirements because police and health officials "will be on the front foot to ensure compliance".
On Saturday, federal Health Minister Greg Hunt announced people arriving from South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia, Eswatini and Malawi are required to enter hotel quarantine for two weeks.
