South Australia still has no local COVID-19 infections despite concerns over several hundred people linked to exposure sites near Adelaide and to an outbreak in Victoria.
About 150 people are in self-quarantine after attending exposure sites in Melbourne, the majority having been to the MCG for an AFL game.
More than 230 people have also been ordered to isolate and get tested after being connected to sites at Tailem Bend, east of Adelaide, where coronavirus-infected removalists from Sydney stopped recently for food and fuel.
SA Health reported no new cases from those tests on Friday but said two new infections had been found in a man in his 50s and a woman in her 40s who had both returned from overseas.
They are among 17 active cases in SA who are all returned travellers in hotel quarantine.
SA has increased its border rules for people returning to the state from Greater Melbourne, Geelong and Bacchus Marsh, requiring them to isolate for 14 days.
Returning residents from other parts of Victoria will not have to quarantine but must undergo tests on days one, five and 13.
Border restrictions also remain in place for southeast Queensland and for people from NSW and the ACT.
Local virus measures have been beefed up with a density rule of one person to every two square metres imposed and private gatherings limited to 150.
Face masks must be worn indoors if venues, such as cinemas or theatres, are above 50 per cent capacity, and at all times in high-risk settings including nursing homes.
Business SA said while a lockdown had been avoided so far, hospitality and tourism industries were bearing the brunt of "seesawing" trading conditions.
"Although the health advice is clear, the changing restrictions with no local community transmitted cases continue to send shock waves through the economy," Business SA Chief Executive Martin Haese said.
"Unlike last time, there is no indication of the timeframe of these restrictions which is providing considerable anxiety for business owners."
Mr Haese said any measures that restrict the ability for businesses to trade must not remain in place for one minute longer than necessary.