Health authorities have praised the efforts of South Australians as the state recorded five new cases of coronavirus.
Four of the infections were linked to a family cluster in northern Adelaide while the other person was still being interviewed by authorities on Tuesday.
South Australian Premier Steven Marshall said the state wasn't out of the woods, urging people to get tested.
"Everybody must play their role in making sure that we stop this disease in its tracks," he told reporters in Adelaide.
"It is very, very important to do that. We have beaten clusters before."
Another 14 people have been classified as suspected cases, as they're at high risk of having the virus.
The cluster has been linked to a quarantine hotel, where it's believed a cleaner contracted the virus from a surface.
Federal Health Minister Greg Hunt has praised South Australians for presenting for testing.
There have been 11,000 tests conducted in the state over the past two days.
He said South Australia was unlikely to face a widespread community outbreak.
"There is more to be done but we are in an extremely strong position," Mr Hunt said.
State health officials have embarked on a testing blitz, with hundreds lining up at pop-up clinics.
Australia's deputy chief medical officer Michael Kidd said the next 24 to 48 hours would be critical.
"Health authorities in South Australia are doing a terrific job, identifying people who may have been in contact with someone who's been diagnosed with COVID-19, arranging to get people tested, arranging for people to go into isolation while they're waiting for their results," he said.
The cluster could derail national plans to open state borders before Christmas.
All states except Western Australia have committed to easing restrictions by December 25.
But Queensland, the Northern Territory, Tasmania and WA have now slammed the gates shut on South Australia.
NSW and Victoria - which has now gone 18 days without new coronavirus infections or deaths - have increased screening for Adelaide arrivals.
This model of enhanced screening of SA arrivals was recommended by the national panel of state and federal medical experts.
"Other states may choose to go further, but they'll have to explain that," Mr Hunt said.
Prime Minister Scott Morrison argues the changes should only be temporary and entire states should not be locked down because of an outbreak in one location.
Australian Medical Association president Omar Khorshid is less concerned about reopening borders by Christmas than he is about reopening society more broadly.
Dr Khorshid is concerned that once families can again get together in big groups, people will quickly forget the lessons learnt throughout the pandemic.
"We need to make sure that we've got enough social distancing, enough restrictions in place, that any outbreak that does happen is small and able to be really quickly controlled," he told the Seven Network.
More Australian Defence Force troops have been sent to SA, while international flights to Adelaide are paused for the rest of the week to ease the burden on hotel quarantine.
The state has re-introduced a range of restrictions, including gyms, recreation centres and play cafes closed for two weeks.
© AAP 2020