Almost two-thirds of Australia's 25 million people were in lockdown Thursday, as the country's faltering bid to bring a virulent Delta outbreak to heel prompted a new wave of restrictions.
The country's two largest cities received a double blow in their efforts to retain "Covid Zero" status, with authorities reporting a record number of new coronavirus infections in Sydney and imposing a sixth lockdown for virus-weary Melbourne.
In total, about 60 percent of the population -- in cities from Brisbane to Ballarat -- are now being told to stay at home.
Until now, Australia has dodged the worst ravages of the pandemic through a strategy of closing borders, lockdowns, mandatory travel quarantine, and aggressive testing and tracing.
But those tools appear blunted in the face of the highly transmissible Delta variant that is now threatening one of the world's last havens from Covid.
Since a Sydney driver was infected with Delta by an international flight crew in mid-June, the area has reported 4,319 cases and clusters have popped up across the country.
After six weeks of lockdown in Sydney, the number of new infections in New South Wales state grew to 262 Thursday, the largest daily tally since the pandemic began.
Health officials said almost all the new cases were in Sydney, but a handful of infections in other districts prompted state premier Gladys Berejiklian to widen stay-at-home restrictions to neighbouring areas.
Five positive tests in Newcastle -- a coastal city of 320,000 people north of Sydney -- prompted authorities to shutter schools and tell residents to stay home for at least a week.
It was a similar story in Victoria, where premier Daniel Andrews said he had "no choice" but to make the "very difficult announcement" to lock down Melbourne and the rest of the state -- little more than a week after the last lockdown ended.
"None of us are happy to be here, none of us," he said, citing the danger posed by eight "mystery" cases that have yet to be traced.
"There is no alternative to lockdown," he said.
"The alternative is we let this run that gets away from us, and our hospitals will be absolutely overwhelmed. Not hundreds of patients but thousands."
That prospect did not deter a crowd of around two thousand protesters -- who unlike most of the city's five million residents who heeded the lockdown -- took to the streets to demonstrate.
Police responded in huge numbers, making arrests and using pepper spray in a bid to disperse the crowd as they marched through Melbourne's city centre for nearly two hours, chanting "no more lockdown" and calling for Andrews to be sacked.
- Under the gun -
Barely 20 percent of Australians have been fully vaccinated, thanks to an acute lack of supply and pockets of vaccine hesitancy.
Five people in their 60s-80s have died in Sydney in the past 24 hours, none of whom were fully vaccinated.
"I cannot stress enough how it's so important for everybody of all ages to come forward and get the vaccine," Berejiklian said.
Prime Minister Scott Morrison has vowed to ramp up vaccine deliveries by the end of the year but put the onus on cities to lock down to contain the spread.
"The virus doesn't move by itself. People staying at home ensures that the virus doesn't move," he said Thursday.