The cases included an aged care worker at Greenway Views and a student from Lyneham High School who tested positive.

ACT Chief Minister Andrew Barr said this was a "serious situation", and the growing number of cases and exposure sites meant the lockdown would be extended by a further two weeks, after advice from chief health officer Dr Kerryn Coleman.

"We do not want to see the numbers continue to grow, we do not want to see exponential growth as we have seen in other jurisdictions," Mr Barr said.

"The best way that we can avoid this is to limit our movement.

"Lockdowns are a proven measure to suppress chains of transmission of the virus."

The lockdown was originally due to lift at 5pm this Thursday.

Mr Barr said arrangements for the lockdown extension were being finalised and this would be announced on Tuesday.

The new cases are in addition to the nine, which had been identified prior to the latest reporting period, bringing the ACT's total number of active cases to 28.

There are more than 6500 Canberrans who have identified as close contacts, which is about 1.5 per cent of the territory's population.

The number of exposure sites across Canberra has increased to more than 45.

Dr Coleman said she expected to see cases rise further.

"This is a very concerning progression, but it's not actually for want of a better word particularly alarming; we are expecting to see cases rise," she said.

"This growth in cases is what we see when we talk about cases coming into a community where there is very little restrictions on its spread.

"So we will see a rise in cases and then as the impact of the lockdown does start to work progressively moving forward, those cases will fall.

"We will get to a point in other jurisdictions that we have seen where the new cases have spent their entire period of infectiousness in quarantine."

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The Greenway Views retirement village has been put into lockdown, after the worker had worked three shifts while unknowingly infectious. These shifts were between August 10 to August 12.

The worker developed symptoms on Friday, August 13, and was tested. The worker had had their first vaccine dose.

Dr Coleman said while this was the first time the ACT recorded a case in an aged-care facility, health authorities had prepared for the scenario over the past 18 months.

"We are working very, very closely with the village to contain this outbreak. Our priority is to minimise the risk of transmission and protect the residents and staff in the village," she said

"We are putting in additional safety measures. We have a team out there at the moment and we are including looking at full PPE for staff."

Mr Barr also said it was his preference that federal Parliament not resume sitting next week unless it was absolutely necessary. He said he had spoken with Prime Minister Scott Morrison and Opposition leader Anthony Albanese about it.

Similarly, he indicated the ACT budget - which had been due to be handed down later this month - would likely be postponed.

ACT Health Minister Rachel Stephen-Smith foreshadowed increased case numbers this week, the school was identified as an exposure site on Sunday.

Another record number of coronavirus cases were recorded in NSW overnight, with 478 local cases of community transmission reported.

An additional seven people have died of coronavirus in NSW since the last update.

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