Victoria has one active COVID-19 case but authorities are concerned about traces of the virus unexpectedly found at a Melbourne waste water facility.
The state has gone 22 days with no new cases.
One patient was cleared in the past 24 hours, leaving just one active case, that of an immunosuppressed person Health Minister Martin Foley said on Saturday was making a "slow and steady" recovery.
A weak-positive case that was under review, that of an elderly woman, has been ruled negative.
Authorities meanwhile have issued a plea for residents and visitors to Altona in Melbourne's southwest from last Monday to Wednesday to get tested if they have even mild symptoms.
Virus traces have been detected in a wastewater sample collected from the Altona sewage catchment on Wednesday.
The result is unexpected because it has been about eight weeks since someone in the area tested positive.
Suburbs in the catchment include Altona, Altona Meadows, Laverton, Point Cook and Sanctuary Lakes.
"It could mean there is somebody in the community that we have missed," Mr Foley said.
He added the detection could have come from someone travelling through the suburbs or virus shedding from an old case.
Mr Foley said the government would say more about the state's border arrangements with South Australia on Saturday.
Victorian communities reliant on SA for shopping and business have lamented separate detections of COVID-19 in sewage which prompted a border closure.
The state's "hard border" with SA came into effect on Thursday night in response to an outbreak in Adelaide, where a cluster now numbers 25 cases.
The closure will be replaced on Sunday by a permit system, however border communities have no idea how it will operate.
It comes as NSW reached two weeks - one complete infection cycle - without a single locally transmitted coronavirus case.
Ten cases of the virus were diagnosed in hotel quarantine in the 24 hours to 8pm on Friday, from more than 16,000 tests.
"While there have been no new locally acquired cases in NSW for the past 14 days, we continue to encourage people to get tested, even if they display only the mildest of symptoms such as a runny nose, scratchy throat, cough or fever," NSW Health's Dr Jan Fizzell said on Saturday.
Locals say they have been thrown into confusion, with one publican labelling the new South Australia border closure "bloody stupid".
Apsley hotelier Robert Carberry told AAP his border community had already dealt with extreme frustration for eight months and just as things were getting back to normal they had been "shot in the neck".
He said many locals had been virus tested 20 to 25 times - once for every weekly shop over the past several months in Naracoorte - just 20 minutes away on the SA side.
This compulsory testing stopped a fortnight ago but residents now face further uncertainty.
Having finished with the SA permit system only to endure another, he said: "It's ridiculous. It's absolutely bloody stupid."
"The people making decisions have no idea what effect those decisions are having on people in border communities."
It is unclear whether Apsley Primary School will open on Monday as it relies on teachers and about 40 per cent of its students being able to cross the border, Mr Carberry said.
The shutdown was prompted by the unexpected detection of virus fragments in wastewater at regional Victorian centres Benalla and Portland.
Both locations are along freight corridors and the results emerged amid Adelaide's growing cluster, sparking a "circuit-breaker" lockdown in that city.
Under the hard border, only freight drivers and those with medical or emergency reasons, as well as people authorised by law, such as child protection officers, will be able to cross.
It's the first time Victoria has shut its border to any state during the pandemic.
The state is preparing for the reinstatement of hotel quarantine, which sparked the second wave, when international arrivals resume on 7 December.
Initially, the traveller cap will be 160 per day.
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