The Australian capital, Canberra, will be rushed to lockdown for a week after registering its first Covid-19 case in more than a year.
It takes effect on Thursday at 5:00 p.m. local time (7:00 a.m. GMT).
The entire Australian capital territory (with around 400,000 people living) had to be closed because authorities do not know how the infected person contracted the virus.
Residents are only allowed to leave their apartments for compelling reasons.
According to reports, queues in supermarkets have acted as closures.
Australia is battling the highly contagious Delta virus, which has put its two largest cities, Sydney and Melbourne, into strict lockdown.
Most areas of New South Wales have been closed and Victoria has had similar restrictions in Melbourne for at least a week.
The New South Wales government said additional military reinforcements may be needed to ensure compliance with the Sydney blockade rules.
The governor of the state Gladys Berejiklian (Gladys Berejiklian) said at a press conference: “We are careful not to spare any efforts for additional (military) resources.”
Around 580 unarmed soldiers are already helping the police to implement quarantine orders in the Sydney area.
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Despite the seven-week lockdown in Sydney, the number of infections is still near the peak. As of Thursday, New South Wales recorded a total of 345 new local infections, including the death of two men in their 90s.
Less than a quarter of Australians are vaccinated. Although the worst of the pandemic was averted, disappointment with the restrictions sparked several large-scale protests against the blockade.