An extra three cases of COVID-19 have been detected in the Australian Capital Territory, all close contacts of the first case that triggered a week-long lockdown.
ACT Chief Health Officer Kerryn Coleman confirmed the new cases on Thursday afternoon shortly after the lockdown began at 5pm.
She said authorities were aware of nine close contacts who had prolonged exposure to the first case.
"We know that three of those have given us additional positive cases, the other six have returned negative tests at this point in time," she told ABC radio.
Territorians are now only allowed to leave home for essential work; healthcare, including to receive a COVID-19 vaccine; an hour of exercise each day; and to buy essential supplies.
Masks have become mandatory across the Territory, general retail has been asked to shut and hospitality venues can only operate takeaway services.
The first case that sparked the lockdown is a man in his 20s who resides in Gungahlin, a northern suburb of Canberra.
Chief Minister Andrew Barr said earlier on Thursday afternoon the source of his infection was unclear.
"This is the most serious public health risk that we have faced in the Territory this year, really since the beginning of the pandemic," he told reporters.
The ACT has remained largely untouched by COVID-19 since its last locally acquired case in July last year.
COVID-19 has also been detected in wastewater.
Queensland has flagged it will close its borders to ACT residents from Saturday, with the state's Premier Annastacia Palaszczuk advising Canberrans they risk being placed in quarantine if they arrive after 1am.
Dr Coleman earlier on Thursday told reporters the lockdown had been called to quickly clamp down on any potential community spread of the virus.
"I suspect its Delta and I suspect the source is from the Sydney outbreak," she said.
"We need to be able to work with the situation, and we need to be able to get everybody to stop moving around."
A number of exposure sites have been identified, , with people who attended these venues at certain times required to quarantine for 14 days and get tested.
Testing capacity will also be ramped up across the ACT with a new drive-through clinic to be established at Brindabella Business Park in the Canberra airport precinct.
Deputy Chief Minister Yvette Berry said parents, where possible, have also been requested to keep their children at home rather than sending them to school.
"If you are an essential worker, if you are experiencing vulnerability, or if for some other reason you can't keep your children at home, then your children can still attend the local public school," she told reporters.
Public schools will spend this week preparing for a potential transition to remote learning should the lockdown be extended.
"We are fully prepared and our teachers are ready to move to remote learning, should that circumstance arise," Ms Berry said.
Mr Barr said he had spoken with Prime Minister Scott Morrison and Treasurer Josh Frydenberg and Canberrans would be eligible for Commonwealth COVID-19 Disaster Payments and business support arrangements.
Upcoming sitting weeks up in the air
Mr Barr said it was currently unclear what the lockdown would mean for the next sitting of federal parliament scheduled for 23 August.
"A starting principle is you want your democracy to continue to function, but it really must be done in a safe way," he said.
"It is too early to say at this point what the next parliamentary fortnight will look like and whether it may or may not need to be postponed."
He said federal politicians would have to themselves consider whether to return to their electorates.
"Clearly there will be some decisions that individual MPs will need to make in relation to what they do during this lockdown period," he said.
"For many going home would be back into a lockdown as well."
With AAP.
