Australia is facing one of its most difficult periods since the beginning of the Covid-19 pandemic as the highly-infectious Delta variant prompts a raft of restrictions across the nation.
Locally-acquired Covid cases were detected in four separate states and territories on Sunday in what Federal Health Minister Greg Hunt described as a "challenging day".
Epidemiologist Nancy Baxter, head of the Melbourne School of Population and Global Health, told ABC Breakfast the nation should be "extremely concerned".
While she warned people not to panic and said she believed Australia would manage to get the virus under control, she warned of a very different second half to 2021 than the first.
"Do I think we are going to be able to live as freely for the next six months as we were the last six months? Probably not," she said.
Professor Baxter envisaged one of the biggest changes being ramped-up mask wearing, which she says will be in place until the nation is fully vaccinated.
Restrictions take effect across the country
Darwin and surrounding regions joined Greater Sydney in lockdown on Sunday as the virus emerged in the community with six cases now linked to a central Australian mine.
Its outbreak was sparked by a positive case of a mine worker at the Newmont-owned Granites gold mine in the Tanami desert, about 540 kilometres northwest of Alice Springs.
More than 1600 people have been ordered into isolation as a result.
"It's our biggest threat yet," NT Chief Minister Michael Gunner told reporters.
In Western Australia, a woman who returned from visiting Sydney picked up the virus, prompting increased restrictions including indoor mask use.
And in Queensland, three local cases were recorded – including an NT miner who was infectious in the Sunshine Coast community and a couple linked to the existing Brisbane cluster, triggering a tightening of density limits.
On Monday, Premier Annastacia Palaszczuk revealed a further two cases, one of which is of the Delta strain, prompting a mask mandate mandate for indoors and outdoors across 11 local government areas in the southeast.
Residents of Brisbane, the Gold Coast, the Sunshine Coast, Logan, Moreton Bay, Ipswich, the Lockyer Valley and the Scenic Rim will have to wear masks unless they're exercising and eating for 14-days from 1am on Tuesday.
Sydney's surging outbreak grew by 30 local cases on Sunday, with the city being warned to expect cases to grow substantially yet again in the coming days.
Virus spread prompts emergency meetings
The nationwide spread of the virus has prompted an emergency meeting of the national security committee, which will be held on Monday.
Treasurer Josh Frydenberg, who will be in attendance, told ABC Breakfast there was now a greater emphasis on getting vaccinated than ever before.
"This is a critical time because we're dealing with the new Delta strain, which is more contagious, more dangerous," he said.
State and territory leaders will also be summoned to an unscheduled national cabinet hook-up as the federal government reacts to the widespread restrictions and the subsequent impact on the economy.
Canberra will also make face masks mandatory indoors from Monday, given the regularity of travel between the ACT and affected parts of NSW.
The outbreaks have prompted a multitude of border tightening measures, including South Australia's closure to all jurisdictions except Victoria and Tasmania.
WA also tightened its border for Queensland, NT and ACT residents, while Victoria added Greater Darwin to its "red zone" list.
All states had already locked out Greater Sydney residents.
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