More than 13 million Australians – about half the population – are in detention after a third state imposed restrictions to curb an outbreak of Delta.
South Australia, home to 1.7 million people, joined Victoria and parts of New South Wales on lockdown on Tuesday.
Its residents will endure seven days at home after the discovery of five infections.
Anger in Australia is growing over the lockdown strategy, with the two largest cities of Sydney and Melbourne facing uncertainty over their opening.
The closures have been closely monitored to ensure that the rules are respected.
Until recently, Australia had been widely praised for its strategy of border closures, quarantine programs and instant lockdowns. It has killed less than 1,000 from Covid.
But the rapid spread of the highly contagious Delta variant has created new challenges and exposed Australia’s low vaccination rate.
Despite entering lockdown late last month, Sydney reported 110 new cases on Wednesday, bringing its current outbreak to more than 1,300 cases.
Residents should not leave their homes except for shopping, exercise and other essential reasons.
Construction sites and specialty retail stores were also closed.
There are fears that Sydney’s shutdown could be extended until September, after modeling showed the city could take months to reach zero new cases.
Many Australians compared their situation to the ongoing reopenings in the UK and US, putting pressure on the federal government.
Last month, a total of seven cities were closed for a brief period.
Australian authorities have pledged to completely eliminate local cases until more people are vaccinated.
Less than 14% of Australians have been vaccinated – the slowest rate among OECD countries.
Prime Minister Scott Morrison’s government has come under heavy criticism, after saying earlier this year that the vaccine rollout “was not a race”.
The slow adoption of the vaccine has been blamed on the government’s failure to secure supplies to Pfizer and public fears about the very rare clotting of the AstraZeneca jab.
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