South Australia has reported no new coronavirus cases as the state begins a six-day hard lockdown to contain a dangerous COVID-19 cluster and Victoria announces border restrictions.
The so-called Parafield cluster remained at 23 confirmed infections on Thursday with three people in hospital in a stable condition.
However Chief Public Health Officer Nicola Spurrier said there were 17 more suspected cases.
She said as a result of contact tracing and testing, 3,200 close contacts of known cases were in quarantine and thousands more were self-isolating.
"With all of the 23 cases and the 17 suspected cases, what we are doing is putting a double ring fence around all of those people," Professor Spurrier said.
"So if you imagine all of those people have had close contacts and then those people have had a close contact, that's where we're up to."
Premier Steven Marshall praised the thousands of South Australians who flocked to testing stations over the past two days with more than 20,000 swabs taken.
He said the statewide shutdown remained absolutely necessary to prevent more widespread community transmission.
"The lessons of surging infections in Victoria and other parts of the world have been learnt," Mr Marshall said.
"COVID-19 is highly infectious, extremely dangerous and very difficult to eradicate once it gets a foothold in a community.
"So we need this circuit-breaker, this breathing space for a contact tracing blitz."
Under the lockdown, people who aren't essential workers are only allowed to leave their homes once each day to buy groceries or to seek a COVID-19 test or other medical treatment. Face masks are required outside the home.
All schools are closed along with universities, pubs, cafes, retail stores, food courts and takeaway food outlets. Regional travel is banned and aged care centres are in lockdown.
Weddings and funerals are also banned along with all outdoor sport and exercise.
Supermarkets, petrol stations, medical centres, critical infrastructure, public transport, airport and freight services, banks, post offices, school and childcare for essential workers and veterinary services are open.
All being well, the six-day lockdown will be followed by another eight days of heavy but less stringent restrictions.
Victoria closes its border to South Australia
The Victorian government, meanwhile, has announced it will temporarily close its border with South Australia.
The government says a 48-hour hard border will be introduced from 11.59pm on Thursday, before being replaced by a permit system from at the same time on Saturday.
More than 300 police officers will patrol the Victorian side of the border, from Mildura down to Portland.
Victorian Premier Daniel Andrews said they knew border communities had had "an incredibly difficult" year, and the decision wasn't made lightly.
"There's simply no way that we can have people who ought not be leaving their home in South Australia doing so and then travelling to our state, not at this time," Mr Andrews told reporters.
"These arrangements will not be in place a moment longer than they need to be."
The decision comes after fragments of the virus that cause COVID-19 were detected in wastewater along Victorian freight routes.
The government says the preliminary positive results at treatment plants in Portland and Benalla are concerning, given no residents in either area are known to have recently had the coronavirus.
"We're asking all locals and visitors in Portland and Benalla with any symptoms at all to please come forward and get tested today," Victorian Health Minister Martin Foley said in a statement.
Under the hard border introduced on Thursday night, only freight drivers, those with legal authorisation or medical, emergency or urgent animal welfare reasons will be able to pass through the border.
The details of the permit scheme are still being finalised ahead of Saturday, but it will allow essential and agricultural workers to cross the border, as well as those shopping for essential supplies, receiving medical care or visiting for compassionate reasons.
With reporting by Jodie Stephens.
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