The Canberra residents will be celebrating in isolation come December 25, as an explosion of COVID-19 cases in their home state of NSW crushed any hope of their first family Christmas in years.

They planned to spend the day with family on Sydney's northern beaches but as that cluster expands to almost 30 cases, they've been forced into quarantine at home.

The sisters visited friends in Manly last weekend and must remain in self-isolation until December 27, as the growing case load led the ACT chief health officer Kerryn Coleman to mandate quarantine for anyone who had returned from the northern beaches since December 11.

"We've still got each other, but it's disappointing we won't be with our parents," Liz said.

It would have been the first Christmas in years they could spend at their family home as they both recently returned from stints overseas.

Liz was rushed home from a volunteering program in Myanmar in early March, and Georgia had to end her time working in Hokkaido, Japan as one the earliest spots coronavirus hit.

"Both of us have had to roll with the punches this year so it's a bit hilarious this is how it's ended," Liz said.

A typical Christmas day would start with a swim before a big lunch with their family, but Liz says they'll make the most of their time at home and hope to recreate the experience with everyone in January.

"We'll probably just cook up a storm and maybe make each other a cocktail," she said.

Entering into isolation in the ACT, where the threat of COVID-19 has been subdued for months, Liz said it was strange knowing her friends were going about their normal lives.

"I've always felt really safe in Canberra. The fact the government are taking these precautions is a good thing but I do feel a bit like a sacrificial lamb," she said.

Although Bec Cotton has her freedom this Christmas, she won't have her family nearby.

Hailing from the northern beaches, Ms Cotton planned to jump on a bus on Friday morning but when the NSW cluster tripled on Thursday night, she decided it was too risky.

"In the early stages I was still planning on going ... I'm going to see family anyway so don't mind if we stay in the apartment the whole time," she said.

"My concern was coming back to Canberra, I've just had job interviews and I [dont' want to] end up having to isolate."

It would have been the first time in years the whole family were together, Ms Cotton said, who had looked forward to seeing cousins who recently returned from overseas.

Ms Cotton has remained positive despite the last minute change of plans, saying perspective was key in a year of constant change.

"My whole vision for this year was very different. This was more of a blip in comparison," she said.

She had quit her job days before the coronavirus lockdown, prepared to move to Norway until restrictions came in and she had to rethink the entire year.

"You've got to count your silver linings," she said.