Officers started randomly pulling over cars at the Federal Highway on Tuesday morning as part of the "random breath testing station" style set-up.

It came after quarantine requirements were put in place at midnight Sunday for anyone returning from greater Sydney, the Central Coast and Wollongong.

Non-ACT residents who have been in the coronavirus affected areas have not been locked-out of the ACT, but have been told not to come to Canberra.

ACT Policing detective superintendent Matt Heather said about 300 cars per hour were being pulled over at random at the roadside set-up similar to a random breath test.

There was a stream of cars passing the police checkpoint on Tuesday and traffic was flowing smoothly.

About seven officers were out on Tuesday, checking whether people were aware of quarantine requirements and directing them to complete an online declaration form and self-isolate at home.

Non-ACT residents will also be directed to self-isolate and will need to make quarantine arrangements.

"There's no turnaround, the ACT doesn't have a hard border. It's a self declaration system and people are required to declare before they enter the ACT and if they have been in a hotspot they are required to quarantine," Detective Superintendent Heather said.

Once a person completes the online declaration form they will be contacted by ACT Health and police to ensure they remain in quarantine for 14 days, regardless of a negative COVID-19 test result.

Detective Superintendent Heather said people could expect to be stopped at any of Canberra's border entries but their focus was on the main thoroughfare from Sydney at the Federal Highway.

"This will come and go as required, it might become a mobile fixture at times and if we need to we can have a more permanent [presence] here," he said.

Detective Superintendent Heather said officers wouldn't have a permanent presence but would be out checking vehicles during peak periods, particularly during the day. Officers would also be stationed at Canberra Airport.

Questions over resources and the power to make the call appeared to delay the decision to man the border, with the decision made against attempting to man the dozens of border crossings between NSW and the ACT.

Detective Superintendent Heather said "it wasn't a mistake" not to have a bigger police presence on the highway as soon as the announcement came into effect on Monday.

"We move our compliance systems up and down as we need," he said.

"The health order got put into effect really recently so we were out and about yesterday and we had a car here and this checking station is going to be manned as we need it to be."

Authorities have called on the community to "do the right thing" and follow the rules, and Detective Superintendent Heather said Canberrans had been "very cooperative" so far.

He praised the Canberra community's compliance, saying police were happy with people following the rules through more than 20,000 quarantine checks conducted to date.

He urged anyone travelling to the ACT from NSW to regularly check for updated requirements as the situation moved quickly.

A further eight cases were reported in NSW on Tuesday, including seven linked to the Avalon cluster bringing the total number to 90.

Anyone who has been in the northern beaches since December 11 is also legally required to isolate upon return to the ACT.

The ACT recorded no new cases of COVID-19 on Tuesday, with just one case in the territory in hotel quarantine.

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Dr Kerryn Coleman said on Monday that ACT residents should re-consider their need to travel in NSW in coming days and be prepared for the requirements to change as more information comes to hand.

She also said Canberrans should be prepared for the current restrictions on travellers from Sydney, the Central Coast and Wollongong to still be in place on Christmas Day, but a final decision would be made in coming days.

Acting Health Minister Chris Steel said the government wasn't considering asking for support from the defence force to help patrol the border at this time.

"We're asking people to use common sense," Mr Steel said when asked if the government was taking a risk by relying on people to do the right thing ahead of long-planned family celebrations.

A huge volume of road traffic was reported on the Hume Highway heading south into the ACT throughout Sunday as the pandemic numbers out of Sydney began to climb.

Concerns exist internally within ACT police that should the current NSW outbreak escalate further and spread and that road travel restrictions be required, the operational workforce required to set up those roadblock checkpoints would be a massive drain on resources.

ACT Policing are already part of the team checking on people in home quarantine, and the more than 100 government officials in hotel quarantine.

One senior ACT police officer, who did not wish to be identified, said that 24-hour ID checks on the border with NSW would be an "enforcement nightmare".

Previously flagged back in March-April when the docking of the Ruby Princess cruise ship in Sydney Harbour and the resulting COVID-19 outbreak sent a massive wave of infection throughout NSW and beyond, the prospect of a border roadblock would have a massive disruptive effect for regular travellers from areas such Queanbeyan, Murrumbateman, Googong and other nearby NSW regional areas.

There are understood to be around 70 road entry points from NSW into the ACT, including four major highways, the Federal Highway, Kings Highway/Canberra Ave; Monaro Highway and the Barton Highway, and nine secondary roads.

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