Dan Suan, a clinic immunologist and researcher at Sydneys Garvan Institute of Medical Research, says the new Omicron variant is much more contagious than any previous strain.

"The only people that are really really protected from the Omicron infection are people who have a normal immune system and have been triple vaccinated," Dan Suan said in a Facebook post.

"Sydney is sleepwalking into a catastrophic disaster in January if we don't do something about it right now."

His warning comes as another 2501 cases were recorded in NSW for the 24 hours to 8pm on Sunday. NSW Health says that takes the total number of active cases in the state to 16,225.

As of Sunday night, there were 261 people in hospital across the state due to COVID-19 and 33 patients in intensive care.

According to the latest vaccination figures released by NSW Health on Monday morning, 94.9 per cent of the state's population aged 16 and older have received their first dose, while 93.4 per cent have had their second jab.

NSW Health is urging people to keep wearing masks indoors, but Premier Dominic Perrottet remains reluctant to reintroduce mask mandates that were eased last week, saying it was time for "personal responsibility".

"We are treating the people of our state like adults," he said on Monday.

In Queensland authorities are recommending masks indoors amid concerns about a potential Omicron superspreader event.

The state recorded another 59 COVID-19 cases in the 24 hours to 6.30am on Monday after 13,595 tests.

Premier Annastacia Palaszczuk says the rising cases are expected with 197,546 border passes issued for people from interstate COVID-19 hotspots in the last week.

She said it's now time to recommend that people wear face masks in all indoor settings, however masks won't be mandated.

There might be 1300-plus new cases but for the first day in three months there was not a COVID-related death in Victoria overnight.

Overwhelming testing demand has created long queues and forced several sites to shut, as Victoria reported 1302 new COVID-19 infections and no deaths.

It is the first day the state has not reported a COVID-related death since September 16, and there are 13,175 active cases in the community.

Tasmania has recorded three new coronavirus infections, taking the island state's number of active cases to 10 since borders reopened last week.

Nine of the cases are being managed at home, while one person is staying at a community management facility.

The three new cases, which were confirmed on Monday morning, include a man in his 30s who arrived in Hobart via Melbourne on Wednesday.

Tasmania had no virus cases when it reopened on December 15 to fully vaccinated travellers from hotspot jurisdictions.

The state government on Sunday announced masks will be mandatory across all indoor settings, public transport and ride shares from 12.01am on Tuesday.

South Australia has recorded 105 new cases of COVID-19, a record number for one day. In total there are now 406 active cases in the state.

Authorities are investigating 65 cases.

There were 13 new cases of COVID-19 recorded in the ACT in the 24 hours to 8pm on Sunday. This is a slight fall from the previous 24-hours when 18 cases were recorded.

According to the ACT government, there are 112 people detected with the infection, bringing the total number of cases in this latest outbreak to 2167.

Health Minister Rachel Stephen-Smith said that there were 40 people with the new, highly-infectious Omicron variant.

Three of the current cases were in hospital, though none of them were on ventilation or in intensive care.

Check out the ACT exposure sites here.

The Northern Territory has opened its borders to travellers who are fully vaccinated against COVID-19, as quarantine requirements for arrivals end.

Travellers now have to return a negative PCR test taken within three days of their arrival in the territory.

The NT's Acting Chief Minister Nicole Manison said three new COVID-19 cases had been recorded in the NT overnight, with one child from Tennant Creek testing positive in Howard Springs.

- with AAP