"Six cases in a 24-hour period is very concerning," Dr Kerryn Coleman said.

"This is serious. We will be reassessing early next week based on the results that we're seeing how far this has spread, how much risk we still think is out there in the community."

The case that sparked the lockdown has been confirmed as the highly transmissible Delta strain of the coronavirus. Lockdown rules have been imposed swiftly.

ACT Chief Minister Andrew Barr said Canberrans had responded well.

"This has been a challenging period for Canberra, but the response to the lockdown today has been very good," he said.

There are currently six active COVID-19 cases in the ACT. One of those cases has not been linked to the others, while the remaining five have all been linked to the initial case.

The first known case in the outbreak was a man in his 20s, who was infectious in the community for four days. The details as to how he contracted the virus have not been released.

Four of his close contacts have since tested positive to the virus.

A 14-year-old student at Gold Creek School also tested positive, but health authorities were still investigating where that infection came from.

The student was infectious at school from Monday, August 9 to Wednesday, August 11.

Authorities were working through 3900 potential close and casual contacts which have been identified from Canberra's check-in app data. Of those, 1862 were confirmed close contacts.

The Gold Creek School campus and early childhood learning centre on August 9, 10 and 11 are considered close-contact exposure sites. The Holy Spirit Catholic Primary School campus is a casual-contact exposure site.

Several university residence halls were sent into lockdown after students living there were determined to be close contacts.

The ACT's testing system has been under intense stress since the announcement of the lockdown on Thursday.

Close contacts need to be prioritised for testing, with authorities urging people not in that category to hold off and stay at home for now unless directed to be tested by health authorities.

There are drive-through clinics at EPIC and Brindabella Business Park, and a walk-in testing site at Weston Creek, which is where children under eight should be taken.

Testing can also be done at Winnunga Nimmityjah Respiratory Clinic, Capital Pathology and Laverty Pathology.

Appointments can be made at YourGP@Crace and Lakeview Medical Practice Tuggeranong.

A dedicated site will be established for people affected by the Gold Creek School exposure sites.

Eligible workers in the ACT can apply for the COVID-19 disaster payment from August 20 on myGov.

The payment provides $750 per week if a worker has lost 20 or more hours of work, and $450 per week if they have lost between eight and 20 hours of work.

People already receiving an income support payment can also claim an extra payment of $200 if they have lost eight hours or more of work, provided they meet the other eligibility requirements for the COVID-19 disaster payment.

A business support package will provide a lump-sum $3000 payment to businesses and $1000 to sole traders who have experienced a 30 per cent reduction in turnover during the week of lockdown.

If you live alone, you can nominate one person to visit throughout lockdown.

The ACT government has provided a list of those deemed essential workers, including anyone working for a business allowed to operate, transport or freight drivers, flight crews, ACT or federal politicians and their staffers.

It extends to anyone who works in health services, funeral services, emergency services or runs a wedding business.

Organisations which provide urgent services include food banks, family violence services and the RSPCA.

The designation also covers those conducting urgent repairs and roadside assistance, waste recovery services, media, essential legal services and building and road construction services.

People who work in food distribution and production, operate an accommodation facility for an approved reason or provide care services are also included.

You can find more detail on who is classed as essential here.

Those who are affected by domestic and family violence are allowed to leave home to seek help during the lockdown.

"If you need help today, or think you'll need help during the seven-day lockdown, because of violence or threatening behaviour at home, contact the Domestic Violence Crisis Service, Victim Support ACT or one of our partner organisations," ACT Victims of Crime commissioner Heidi Yates said.

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