The country's COVID-19 death toll rose to 155 and the southeastern state of Victoria reported more than 450 new infections in the last 24 hours.

A clearly concerned Victoria Premier Daniel Andrews said ten people aged between their 40s and 80s had died, of which seven deaths were linked to outbreaks in aged care facilities.

It is the worst loss of life from the virus in Australia since the disease first emerged, according to a tally compiled by AFP.

Australia has dodged the worst ravages of the pandemic so far, logging just 14,000 cases in total -- fewer than many harder-hit countries see in one day.

But a second wave of infections is testing the nation's much-lauded response to the contagion.

The number of new cases has remained stubbornly high in recent days despite five million people in greater Melbourne spending the last two weeks in lockdown.

Masks are mandatory in the city and Victoria is virtually sealed off from the rest of the country.

Police and the military are guarding state borders and visiting homes to enforce quarantine orders.

Still, 459 fresh cases were reported in Victoria on Sunday -- up from 357 on Saturday. Around a dozen more were recorded in other parts of Australia.

"These things change rapidly, but we have to say these numbers are far too high," Andrews said.