With about 15 million people in the three states, or 60% of Australia's population, under a strict lockdown, the country also reported five coronavirus-related deaths, one of the highest this year.
Australia saw a record daily number of new coronavirus
cases this year on Saturday, with the country's most populous states of New South Wales, Victoria and Queensland recording a total of 361 cases of the highly infectious Delta variant.
With about 15 million people in the three states, or 60% of Australia's population, under a strict lockdown, the country also reported five coronavirus
-related deaths, one of the highest this year.
NSW suffered its worst pandemic day, reporting 319 new locally acquired COVID
-19 cases, with Sydney and neighbouring regional centres spanning 200 km (120 miles) of coastline under a stay-at-home order for six weeks already.
There are 345 people admitted to hospital in NSW, with 56 in intensive care and 23 under ventilation.
NSW authorities, who had been reluctant to put Sydney into a lockdown, said lack of observance of rules has been a problem.
"What we have happening right now is some people are not complying," NSW Health Minister Brad Hazzard said.
"Just stay at home - that is the circuit breaker. Stay at home and get vaccinated."
Neighbouring Victoria saw the highest daily jump in cases this year, with 29 new infections, as the state remains under a snap seven-day lockdown imposed earlier this week, the state's sixth since the start of the pandemic.
Victoria Premier Dan Andrews urged people to follow the public health rules that allow residents to leave their house only for essential work, shopping, care, vaccination or two hours of outdoor exercise.
"This Delta variant spreads so fast," Andrews said. "We don't have enough of people vaccinated, we will finish up with younger people in the hospital, otherwise fit and healthy people. Our system will be overrun if we don't bring this under control."
Queensland recorded 13 new cases, with all but one isolating while infectious, bringing hopes that the eight-day lockdown in parts of the state will be lifted as planned on Sunday afternoon.
With just over 36,000 COVID
-19 cases and 937 deaths, Australia has avoided the high caseloads of other developed countries, but its vaccination figures are among the lowest, with only 20% of people aged over 16 fully vaccinated.