Victoria has declared a state of disaster and imposed new lockdown measures after a surge in coronavirus infections.
Under the new rules, which came into effect at 18:00 (08:00 GMT), residents of the state capital Melbourne are subject to a night-time curfew.
There will be further restrictions on residents' ability to leave home.
Australia has been more successful than many other countries in tackling Covid-19, but cases are rising in Victoria.
The state - Australia's second most populous state - now accounts for many of the country's new infections in recent weeks, prompting the return of lockdown restrictions in early July.
But on Sunday Premier Daniel Andrews said the measures were working but too slowly. "We must go harder. It's the only way we'll get to the other side of this," he told reporters.
The new rules will remain in place until at least 13 September, Mr Andrews added.
On Sunday, Victoria reported 671 new coronavirus cases and seven deaths. Those increases brought the totals to 11,557 infections and 123 deaths.
The night-time curfew is being implemented across Melbourne from 20:00 to 05:00.
The only valid reasons for leaving home during these hours will be work, medical care or care-giving.
Melbourne residents will only be allowed to shop and exercise within 5km (three miles) of their home. Exercise outside of the home will only be allowed for one hour at a time.
Only one person per household is allowed to shop for essentials at a time.