Murrumbidgee Local Health District chief executive Jill Ludford said residents who do go to Sydney for the Christmas period may have to isolate on their return as public health advice changes to keep up with the outbreak.

"Yes, we have Christmas. And we have eased restrictions, which means that people can now move around more freely across our region. But we have to be even more vigilant now that we have the situation in Sydney," she said.

NSW recorded 15 locally acquired cases of COVID-19 in the 24 hours to 8pm on Sunday night - down from 30 new cases confirmed on the previous day - all of which are linked to the Avalon cluster in Sydney's Northern Beaches that now numbers 83.

NSW public health officials say investigations continue into the source of the cluster, which has thrown many residents' Christmas plans into disarray.

There were a record 38,578 tests reported over the same 24 hour period, marking the state's highest number of COVID-19 tests ever conducted in one day.

Ms Ludford said people in the Greater Sydney, Illawarra Shoalhaven and Central Coast regions had been asked by NSW Premier Gladys Berejiklian to restrict their movements, but acknowledged there were "a lot of people from Sydney already here" in the Murrumbidgee.

"We really ask people to reconsider their movements, because it is really important we keep our region safe. And again, if people have to travel, then they need to make sure that they are well when they leave and that they monitor their symptoms carefully," she said.

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"If you're travelling through Sydney to another destination, then the messages in the airport are about those hand hygiene, socially distancing ... always managing your own luggage, so that you don't have other people's hands on your luggage. And wearing masks at all times both in the airport, as well as on the plane."

When she was asked if she would support a "ring of steel" travel border around Sydney to restrict movement to regional NSW, Ms Ludford said she was confident in the current advice provided by the state's chief health officer Kerry Chant.

"I will absolutely go by the decisions that she recommends through to government. And I'm confident that she and the team around her are making really good decisions," Ms Ludford said.

'Stay at home' orders are in place for the Northern Beaches local government area that will continue until 11.59pm on Wednesday, December 23, with NSW residents awaiting a change in restrictions if health authorities are able to control the outbreak.

Ms Ludford said the MLHD has introduced its own new restrictions, in line with NSW Health, which will also be reassessed before Christmas Eve.

No visitors will be granted access to MLHD's Residential Aged Care facilities until at least 11.59 pm on December 23.

Visitors undertaking essential caring functions will be given consideration, but must wear a mask and will need to speak to their facility's manager.

Visitors to MLHD's hospital acute care are limited to two people and all visitors are required to wear a surgical mask, while visitors from Greater Sydney, Illawarra Shoalhaven and Central Coast will be excluded from all Murrumbidgee health sites until further notice.

Ms Ludford said Wagga health authorities would be prepared for another outbreak in the Murrumbidgee should cases seed here from the coast.

"Over the weekend, our public health unit, our virus detectives, they've been helping out with the contact tracing in Sydney. So we've got a really good workforce here that can scale up to be able to do that work early," she said.

"And of course, our intensive care capability can be ramped up at any time."