Scott Morrison has assured Australians the country is not facing the same sort of challenges it endured when the coronavirus first arrived in early 2020, as a new variant emerges.

The prime minister says the emergence of Omicron is a fast-moving issue but the government will continue to be guided by the best possible medical advice.

"This is not like it was back in February and March and 2020," Mr Morrison told reporters in Canberra on Sunday.

"We now have good knowledge, good advice, the uncertainties are not like they used to be, we have good systems which have been proven."

Australia has shut its borders to nine southern African countries and states have brought in new rules for international arrivals amid concern over Omicron.

Victoria's chief health officer Brett Sutton says not enough is known about Omicron but it appears to be a very transmissible variant.

"It certainly seems to have spread very quickly in southern Africa and in the Republic of South Africa in particular," he told reporters in Melbourne.

"Numbers have been increasing evidently over a short period of time, it has become the predominant variant in that country already in a very short period of time."

Even so, Opposition Leader Anthony Albanese congratulated state governments for their swift action.

"This strain could cause a real problem," he told reporters in Melbourne.

"We know that with Delta it spread very quickly, and we need to take whatever measures are necessary."

NSW Premier Dominic Perrottet said urgent genomic sequencing is being undertaken to establish whether Omicron has already reached Sydney.

Two people who arrived from Africa overnight tested positive to the coronavirus on arrival and are now being investigated to see whether they have the Omicron variant.

In total, NSW reported 185 new infections on Sunday, but for a fourth day in a row, no new deaths were reported.

In Victoria, 1061 new cases were announced and four more virus-related deaths, while there were seven new infections in the ACT.

There were also four new cases detected in the Northern Territory, where the remote community of Lajamanu will stay in lockdown until December 11 after the virus was detected in wastewater.

There were no new infections in South Australia after reporting three on Saturday.

NSW, Victoria and the ACT have introduced a three-day home quarantine requirement for international arrivals.

At this stage it means travellers from Japan and South Korea can enter Australia without needing to quarantine from December 1 as planned, Trade Minister Dan Tehan says.

However, the Morrison government is keeping a watchful eye on developments surrounding the Omicron variant.

Mr Tehan told Sky News' Sunday Agenda program from Geneva that he believes the government hast got the balance right at this stage.

"But obviously there is more work to be done in understanding this new variant and the potential impacts it might have."

Mr Tehan travelled to Switzerland for a World Trade Organisation ministerial meeting, only to find it had been cancelled because of the clampdown on travellers from the southern African states.