South Australia has dodged an immediate lockdown after confirming five local COVID-19 infections, but the SA's peak business group says the state remains on a "knife's edge" in its battle to contain the virus.
The new cases involve a miner, who recently returned from the Northern Territory, his wife and three of their children, all aged under 10.
"While this is a very concerning turn of events, we are very relieved this person and this family have been at home since Saturday," Mr Marshall said on Wednesday.
"South Australia is not going into a lockdown and I think many people will be extraordinarily relieved about that."
The premier said the family had all been transferred to Adelaide's dedicated facility for positive coronavirus cases.
Their infections were regarded as "linked transmissions" from the NT's mine exposure site.
The other 28 miners who returned from the same facility near Alice Springs have also been in isolation since arriving in SA and are being retested.
All have returned negative results so far.
Chief Public Health Officer Nicola Spurrier said officials had moved to require anyone on the same Alice Springs to Adelaide flight as the infected miner on Friday, to go into isolation.
More than 100 people who were on board VA1742 have already been contacted with a small number still to be notified.
Checking is also underway to identify any possible contacts at Adelaide Airport and at a suburban takeaway food outlet the man visited on his way home.
Both those locations are considered low risk.
Professor Spurrier said while the outbreak was regarded as contained at this stage, more work remained to be done and officials did not want the Delta strain of the virus to become widespread in the community.
"What we're seeing with this Delta variant is there's almost a 100 per cent hit rate for close contacts," she said.
Business SA said the five new cases had "shaken" the state's confidence and SA remained at high risk of "leakages".
"South Australia is walking on a knife's edge at the moment, and we must all be vigilant to ensure this does not go any further," Chief Executive Martin Haese said.
"We must do everything we can to avoid going into a lockdown like we have seen in most other jurisdictions this week."
In response to the new cases, SA's transition committee has reduced the number of people allowed at family gatherings to just 10.
Premier Marshall said people were also being advised to work from home where possible, wear masks when out in public, use QR codes, get vaccinated and observe social distancing.
"We can see the consequences of getting this wrong. We don't want a lockdown in South Australia," the premier said.
Amid reports of panic buying across SA supermarkets, the premier said there was no need for such action.
The shop workers' union said people rushing to supermarkets would only increase the risk of community transmission.
"There is no need for South Australians to panic about stock levels in supermarkets and there is absolutely no excuse for abusive behaviour towards retail workers," SDA state secretary Josh Peak said.
© AAP 2021