But the territory's Chief Health Officer Kerryn Coleman stopped short of introducing new border restrictions on Friday, confident there was no immediate risk to the ACT.

ACT Health Minister Rachel Stephen-Smith provided the most significant indication to date that the territory was looking to tighten restrictions with NSW.

She said the ACT was monitoring the situation in NSW very carefully and was making plans in case a regional bubble with places such as Queanbeyan was needed. She warned Canberrans and residents from surrounding towns to be prepared.

"We're continuing to prepare for multiple scenarios," Ms Stephen-Smith said.

"As we continue this planning, we are asking the community to be aware that the situation could change very quickly, and to be prepared to respond to any increasing restrictions or changes to travel advice.

"In the event of tightening restrictions in the ACT we will work very closely with surrounding communities to ensure that people understand the implications of any new requirements or restrictions that might be put in place."

Earlier on Friday, it seemed likely that the ACT was going to implement a regional bubble. It followed remarks by NSW's Chief Health Officer Kerry Chant, who said the Covid crisis in south-west and western Sydney had developed into a "national emergency".

Ms Stephen-Smith said health authorities were very concerned by Dr Chant's statement and she thought restrictions on parts of regional NSW would be implemented.

"When the NSW Chief Health Officer comes out and says she has advised her government that she now considers the situation in Sydney to be a national emergency that obviously heightens everybody's concern about the state of affairs in Sydney," Ms Stephen-Smith said.

"I have to say at that time, I thought we would probably be in a situation where we would be at least looking at some regional areas where we might be getting advice from NSW."

It came after there were a string of new exposure sites in Goulburn and Marulan, including Bunnings Goulburn and KFC Marulan.

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Ms Stephen-Smith said the ACT government had worked through plans with surrounding NSW local councils.

"What we're really trying to do now is to make sure that we have all of that detail in place ... so that if we have to hit the go button on effectively creating some kind of regional bubble that we have all of those arrangements in place as much as we possibly can," she said.

Ms Stephen-Smith said there was not a defined trigger point as to when the ACT would implement a regional bubble, saying it would depend on the circumstances.

"If we start to see cases in regional NSW but they're contact traced really early and they're small exposure sites as has been the case with Goulburn and Marulan, then that's a different matter," she said. "If we start to see seeding, we start to see community transmission then that will be a different matter altogether.

"It will depend also on whereabouts in NSW ... it's a big place. Some regions are close to the ACT and some regions are a fair way away from the ACT.

"We keep a much closer eye on the regions that are closer to us."

ACT authorities have considered the possibility of a regional bubble over the past year.

Given the high volume of travel for work between the ACT and surrounding NSW regions such as Queanbeyan-Palerang and Yass Valley, it would be "virtually impossible" to implement a hard border, Ms Stephen-Smith said.

But she said authorities were considering a number of issues, including how a bubble could be implemented and how big the bubble would need to be.

"Obviously, there are some places like Queanbeyan and Sutton and Murrumbateman where there is a lot of flow," Ms Stephen-Smith said.

"There are other places like Goulburn where we know that people do commute to the ACT but it's a far smaller number and of course Goulburn is much closer to Sydney.

"It's actually working through all of those issues to understand what our different options look like and how we would describe that to people when we go out.

"Because if we do have to do this, and we do have to go out to people to ask people in our surrounding region to do something, we need to be really clear who we're asking and what we're asking them to do."

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