NSW has confirmed another nine cases of the Omicron COVID variant as concern grows for a superspreader event at a Newcastle nightclub.

The state had 536 virus infections on Monday, continuing an upward spiral from recent days.

With the festive season well underway, NSW Health is battling to contain several large transmission events, including infections of the rapidly spreading Omicron variant – with 64 cases of the strain confirmed in NSW by Monday.

“There were nine new cases confirmed with the Omicron variant overnight, and more are expected as results of genomic testing are confirmed,” NSW Health said on Monday.

The number of infections linked to an outbreak at The Argyle House nightclub in Newcastle leapt from 24 to 84 overnight. Authorities warn that “a number of these cases are likely to be the Omicron variant”.

Four people who partied at the club last Wednesday had COVID-19. Their infections are linked to the outbreak stemming from a Sydney harbour cruise of 140 people on December 3.

All 680 people who checked into the Newcastle nightclub with a QR code between 9pm Wednesday and 3am Thursday are close contacts and must immediately get tested and isolate for seven days.

The Hunter New England Health District confirmed its first Omicron case on Sunday, in a recently returned traveller from Britain. She is not connected to the nightclub outbreak.

Hunter public health controller David Durrheim said the woman was isolating at home.

NSW Health said an investigation was underway into the transmission of the virus and more Omicron cases were expected in the Hunter region.

The Argyle House cluster is one several to emerge in recent days in NSW.

At least 44 cases have been linked to a pub trivia night at the Oxford Tavern in Petersham, in Sydney’s inner-west – authorities suspect several cases of the Omicron strain among the infected.

There were at least another 17 infections at the Golden Sheaf Hotel in the harbourside suburb of Double Bay last Friday.

Last week, NSW Health sounded the alarm about a spike in COVID clusters driven by festive events and pre-Christmas socialising.

“The transmission in these types of settings is contributing to the increase in cases in NSW and we urge people not to attend social functions if they have any symptoms, even if mild,” Dr Jeremy McAnulty said.

Elsewhere, the wait time to receive a COVID-19 booster shot has been reduced from six months to five to help tackle the new strain.

Epidemiologist Raina MacIntyre from the University of NSW Kirby Institute said adults needed to start thinking about three shots of a COVID-19 vaccination as being the number required to be fully vaccinated.

“Thinking you’re fine with two doses, if Omicron is going to spread in Australia, is a false sense of security,” she told ABC radio on Monday.

Early data indicated that even after three doses antibody levels “start to wane pretty quickly as well”.

“It may well be that we need another fourth dose within less than a year,” Professor Macintyre said.

There are concerns in the NT about further spread of its coronavirus outbreak. Photo: ADF

‘A big number’: 17 more case in the NT

The Northern Territory has detected 17 coronavirus cases as a cluster linked to a pocket of overcrowded homes continues to grow.

More than a dozen infections have been diagnosed among households on four streets in East Katherine, 320 kilometres south of Darwin.

“Of these 14 cases, eight are children under 12 … and there is one 70 year-old female,” Acting Chief Minister Nicole Manison said on Monday.

“It’s a big number but it’s a number we expected.”

The other five cases are adults aged 20-49.

All 14 cases will be moved to quarantine at Howard Springs, south of Darwin.

A teen and a man in his 70s at the facility have also tested positive.

It brings the outbreak to 87 cases.

Ms Manison said outbreak might have also spread to Timber Creek, near the Western Australian border.

An infected Binjari man who visited the town, about 225 kilometres east of Kununurra, has returned a “provisional positive” test result and is now in isolation.

Authorities were expecting to find more cases, she said.

A traveller who arrived on an international flight from Singapore was also diagnosed with the virus.

-with AAP