A Covid outbreak in Sydney linked to the highly contagious Delta strain has grown to 110 cases, while infections emerged in other parts of the country.
Small outbreaks have been recorded in the Northern Territory, Queensland and Western Australia states.
This is the first time in months that cases have emerged in various parts of Australia.
Federal and state governments will hold emergency talks about the situation on Monday.
Treasurer Josh Frydenberg said it was “a critical time” for the nation, as various states shut borders and enacted new restrictions to prevent further spread.
“I think we’re entering a new phase of this pandemic, with the more contagious Delta strain,” Mr Frydenberg told ABC News on Monday.
The escalation in Covid infections has prompted lockdowns in the cities of Sydney and Darwin, as well as restrictions across four states.
The situation remains most concerning in Sydney, where some 5 million residents are subject to a stay-at-home order.
The New South Wales (NSW) state government on Sunday expanded a lockdown to cover all of Greater Sydney, the Blue Mountains, Central Coast and Wollongong.
Many businesses and venues have been ordered shut.
“Given how contagious this strain of the virus is, we do anticipate that in the next few days, case numbers are likely to increase even beyond what we have seen today because we are seeing that people in isolation, unfortunately, would have already transmitted to all their house contacts,” said NSW Premier Gladys Berejiklian on Sunday.
While cases in Queensland and Western Australia have been traced to the Sydney outbreak, the infections in the Northern Territory were of an unrelated strain.
Meanwhile, Virgin Australia said on Sunday it contacted passengers and crew on five recent domestic flights, after a crew member had tested positive in Melbourne.
The outbreaks have prompted some inter-state and international border closures.
New Zealand paused its quarantine-free travel bubble with all of Australia until at least Tuesday because of the latest outbreak.
The travel corridor between the two neighbours was opened in April. Travel between New Zealand and specific Australian regions has been closed for short periods as outbreaks occurred, but this is the first time the bubble has been shut with all of Australia.