Of the new cases, six were linked to known infections, while investigations are ongoing for the remaining four.

There are also two cases with no known links at this stage.

Two of the newly announced cases were in quarantine for all of their infectious period, with six being infectious in the community, and four under investigation for their infectious status.

The number of people in hospital with Covid in the ACT has risen to 12, three of those in intensive care.

Eleven of those in hospital were unvaccinated, while the other had only had one dose of the vaccine.

While the outbreak in the ACT had reached 250 total cases as of Sunday and there were 12 new cases reported on Monday, one case has been reclassified, pushing the total number of cases to 261.

Twenty-five people have recovered since being infected, leaving 236 active cases in the territory. The source of 20 of those infections is yet to be identified.

There were 2262 tests carried out in the previous 24 hours.

ACT Chief Health Officer Dr Kerryn Coleman said it was possible there had been more than one introduction of Covid into the ACT from previous virus hotspots.

ACT Chief Minister Andrew Barr said police had carried out 284 traffic stops in the past day, along with issuing five directions.

There were also 133 business compliance checks, following on from new business requirements for some industries to only provide click-and-collect or delivery options.

Mr Barr also announced 16- to 29-year-olds will be able to make a booking for Pfizer vaccines in coming days.

Since registrations for the cohort opened, 25,000 people in that age group have come forward to register their interest in receiving the vaccine.

Appointments are expected to be available for that age group from late October or early November - however the AstraZeneca vaccine is already available.

The Chief Minister said he hoped that by the time the country reaches the 80 per cent target for people having received both vaccine doses, the ACT will be at 90 or even 95 per cent.

He added that the coming spring would be difficult in the ACT.

"Twelve cases is significantly better than 1200, but it's still concerning there are cases infectious in the community without links," he said.

Of the total cases, the age profile of the infections has skewed much younger than for previous strains of the virus. 34 per cent of those infected in this outbreak have been under 18, while another 50 per cent have been between 18 and 44 years old. 13 per cent are 45 to 64 years old, and just 3 per cent are over 65.

A decision on whether the ACT will end its lockdown as scheduled on Thursday is due to be announced in coming days.

Mr Barr said he hoped to make an announcement on the future of the lockdown on Tuesday, following a crisis meeting on Monday.

Dr Coleman said there were four new cases linked to the Mirchi Indian restaurant, while the number of cases linked to the Fiction nightclub has risen to 50. The Bright Bees cluster has increased to 28 total cases.

On Sunday it was confirmed that a person had visited the Ainslie Village social housing complex while unknowingly infectious.

The complex has since been listed as a close-contact exposure site, which Mr Barr said was concerning.

"If the virus gets into high-risk and vulnerable settings, it can be a big setback for pandemic management," he said.

Dr Coleman said two people linked to social housing complexes had tested positive for Covid on Monday morning.

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As the ACT's lockdown enters its third week, the number of Canberrans in quarantine has fallen dramatically.

There are now about 600 people who have self-identified as close contacts and are now in quarantine, well down from the more than 20,000 in the early stages of the lockdown.

There are also 3200 Canberrans who are considered casual contacts.

Health Minister Rachel Stephen-Smith said a decision had been made on Sunday afternoon to release close contacts associated with clusters at Gold Creek School, Harrison School and Lyneham High School from quarantine.

However, there had been delays in health authorities getting in touch with those in quarantine and allowing them to come out of isolation.

Ms Stephen-Smith said there were less than 200 callbacks for quarantine release still in the backlog and the government hoped to have them all completed by Monday afternoon.

Across the border, NSW recorded 1290 new cases of Covid in the 24 hours to 8pm on Sunday, a new single-day record for any Australian jurisdiction during the pandemic.

Mr Barr said the news that fragments of Covid had been detected in sewage over the weekend in Cooma was concerning, given a fall in the number of tests conducted in the region.

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