Acting Health Minister Chris Steel said that while the coronavirus situation on Sydney's northern beaches was "looking optimistic", ACT chief health officer Kerryn Coleman had decided the growing cluster still posed a risk to the territory.

The ACT's hotels association said the news, while not unexpected, was "devastating" for the industry, as it called for clarity on the specific criteria that would allow the 14-day quarantine requirement for returned NSW travellers to be lifted.

NSW recorded eight new locally acquired cases on Wednesday, as Premier Gladys Berejiklian announced Sydney would be effectively split into three regions over the Christmas period as part of "modest changes" to the city's coronavirus restrictions.

The ACT reported no new cases in that period, despite a record 1300 tests.

More than 450 people will be spending Christmas in isolation in Canberra after returning from one of the declared NSW hotspots, including 39 from the northern beaches.

While no firm date had been set for lifting the restriction on travellers entering from NSW, Mr Steel said it was likely to remain until at least January 1.

He said setting the general timeframe would provide some certainty for the community and businesses over the festive period.

"I know this will be disappointing news for many people who wanted to see family and friends over the Christmas period," Mr Steel said.

"The reality is that the virus and the whole pandemic is far from over. We need to take the action that we can to reduce the risk of transmission."

The Avalon cluster has grown to 97 after seven new cases linked to the outbreak were reported on Wednesday.

With NSW authorities still trying to locate the source of the outbreak, Ms Berejiklian announced "very modest" changes to restrictions across Sydney on December 24, 25 and 26.

A 10-person limit on visitors will remain in place for households in Greater Sydney, although extra children aged under 12 will be allowed on those three days. The strict 10-person limit will be reimposed on December 27.

The northern beaches, where the outbreak is centred, will be effectively split in two on Christmas Eve, Christmas Day and Boxing Day.

Residents in the northern section of the area, which Ms Berejiklian described as the "epicentre" of the cluster, will remain in lockdown and won't be allowed to leave, although they are permitted five visitors from the region in their house over the three-day period.

In the southern section of the northern beaches, in suburbs such as Manly and Dee Why, households will be allowed up to 10 visitors over the Christmas period.

A decision on restrictions for the southern section beyond December 27 will be made in the coming days.

While there is no ban on travel from Sydney to regional NSW, Ms Berejiklian asked people to be extra cautious.

The ACT's announcement on Sunday of restrictions on travelers from NSW triggered mass cancellations at Canberra hotels, as visitors scrambled to rearrange their Christmas plans.

Australian Hotels Association ACT general manager Anthony Brierley said millions of dollars had been lost in the past three days, with hotels reporting numbers of cancelled bookings on par with the March shutdown.

Mr Brierley said that while it was expected the restrictions would remain through the festive period, the Wednesday's confirmation was still "devastating".

He said rather than "obfuscation" from ACT authorities, the industry desperately needed clarity on the specific criteria that would enable the border restrictions to be safely lifted.

Mr Steel said Dr Coleman, who wasn't present at Wednesday's press conference, would consider a number of factors before deciding whether to lift the travel restrictions.

This included daily case numbers, the degree of movement between the ACT and NSW, testing rates and the prevalence of community transmission of the virus.

Earlier on Wednesday, Dr Coleman wanted NSW testing numbers to remain "reassuringly" high and for minimal movement between Canberra and hotspot areas.

"If there is more movement I'm more concerned, if there's less movement I'm less concerned," she told ABC Radio Canberra.

She said it was most important all new cases were identified and linked to the Avalon cluster, which has been the case for the majority of infections so far. She said that meant new infections were already in quarantine and therefore didn't pose a risk of infecting others.

"It's not necessary to see no cases in the NSW area; it's the details about those cases and the settings in NSW which would allow transmission to occur undetected," she said.

Police are randomly checking cars at Canberra's northern border on the Federal Highway in a random-breath-testing-station-style operation.

There is no hard border closure with NSW, which means a resident coming from a COVID-19 hotspot is allowed to enter the ACT and will not be turned around by police.

They are required to fill out a declaration form and self-isolate. If a person enters and is not a Canberra resident police say they will need to make their own quarantine arrangements.

ACT Health says non-ACT residents should not be coming if they have been in greater Sydney, the Central Coast or Wollongong.

ACT Policing Detective Superintendent Matt Heather said police were advising people of their need to complete the declaration but wouldn't "sit there with them" to ensure it was done.

"They have that obligation to self-declare and we're just encouraging people to do so," he said.

Detective Superintendent Heather said there would also be mobile patrols of Canberra's other borders.

Following a huge spike in demand for the COVID-19 hotline on Monday, when 3000 calls were answered, the service's operating hours have been extended.

The line is now open from 7am to 9pm. Dr Coleman said this would be reviewed daily and remain as long as demand remained high.

On Tuesday 1760 calls were answered.