Two overseas travellers have been infected with the new Omicron COVID-19 variant of concern, NSW Health has confirmed.
Both passengers came to Sydney from southern Africa on Saturday evening.
They underwent testing on arrival and tested positive for COVID-19 late last night.
NSW Health said urgent genomic testing today showed they had the Omicron variant.
The two positive cases, who were asymptomatic, are in isolation in special health accommodation. Both people are fully vaccinated.
The two passengers were among 14 people from southern Africa who arrived on Qatar Airways QR908, Doha to Sydney.
The remaining 12 passengers from southern Africa are undertaking 14 days of hotel quarantine in the special health accommodation.
About 260 passengers and air crew on the flight are considered close contacts and have been directed to isolate.
NSW Premier Dominic Perrottet earlier today warned the COVID-19 pandemic was not over, as the urgent genomic sequencing was under way to establish whether the Omicron strain had already reached Sydney.
Twenty-nine people who had been in one of the nine southern African countries subject to elevated restrictions landed in Sydney across two flights on Saturday evening. They are all in hotel quarantine.
The two positive cases were on the same Qatar Airways flight from Doha that flew in at 7pm.
Mr Perrottet said it was a reminder that the pandemic was not over, and described his approach as precautionary.
However, he warned that it must be expected that the variant would spread throughout the world.
Although he's ordered all international arrivals to quarantine at home for 72 hours, 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 three-day quarantine order is on top of a federal government requirement for travellers to enter quarantine for two weeks if they've been in South Africa, Lesotho, Botswana, Zimbabwe, Mozambique, Namibia, Eswatini, Malawi or the Seychelles within the past 14 days.
Health Minister Brad Hazzard said not much was known about the new strain, though it may be more transmissible than Delta.
In particular, the effectiveness of current vaccines against Omicron is still being established, he said.
Anyone already in NSW who has been in the nine southern African countries within the previous 14 days must immediately be tested, isolate for 14 days and contact NSW Health.
- with AAP