There are 66 border crossings into the territory, making any shutdown one of the most complex in the country.

The government says while the closure of the ACT and NSW border would be an absolute last resort, it is preparing for the possibility.

It is also considering the merit of a regional bubble, which would effectively bring towns like Queanbeyan into the ACT.

Such a proposal would need the cooperation of NSW.

Chief police officer Neil Gaughan said a hard border would be extremely challenging to enforce, with both NSW and ACT's police forces already stretched.

"I think sometimes we're underestimating the impact [the pandemic] is having on law enforcement," he said

"Not just around border closures but actually ensuring that quarantining is maintained, and it's business as usual. The territory is basically opened up again, which is great, but we've got to police that."

In the event of a border closure, all road entrances would have to be monitored by police, while fire trails may be blocked with boulders.

This includes four major entries of the Barton, Monaro and Federal Highways along with Canberra Avenue.

There are then nine minor road entrances including Lanyon Avenue.

In the event of a hard closure, a permit system would be in place for those who need to enter for essential reasons.

"One of the things I need to focus on is ensuring if we do something like that how do we actually balance that with the rest of the business we have to do," he said.

Any closure of the ACT and NSW border would be among the most complex in the country.

"I don't know how many [jurisdictions] would have over 60 border crossings," chief police officer Gaughan said.

"Admittedly a lot of those are small fire trails which we could probably close through other means besides having people at them.

"But we're about to go into spring and summer and obviously what we do know is there are potential impacts on the ability of [firefighters] to deal with bushfires.

"It's difficult, we are an island within a large jurisdiction ... I think it's really difficult for us to do."

Chief health officer Kerryn Coleman said even with a border closure, the ACT would never be able to stop the flow of people from NSW into the territory.

On average about 47,000 vehicles enter and leave the ACT border in 24 hours, while about 25,000 people in NSW work in the territory.

About 4000 Canberrans cross the border to work in NSW. About 10 per cent of healthcare and social assistance workers live outside the ACT.

"We have freight moving through, we have large numbers of workers, we have a lot of people moving through that border," Dr Coleman said.

"It's not realistic to put in place a border and expect we can go back to normal."

A hard lockdown would only be considered when there were significant levels of community transmission within the ACT, putting pressure on health services.

"Really we would just want to stop the ability for any more cases to be appearing in the ACT," Dr Coleman said.

"We will never be doing that on its own, at that point we would have needed to put in place significant community restrictions again, similar to what we are seeing in Victoria."

However what would be more likely would be public health directions restricting people's movements without border patrols.

"[In that case] what we would monitor for is significant increase in cases in the surrounding region," she said.

"We would look for increasing numbers in outbreaks and clusters, but in particular increasing number of cases where we can't identify the source of exposure."