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The southeastern state recorded 108 new cases on Saturday, up from 66 on Friday and more than 70 new cases in each of the previous four days, forcing authorities to reimpose lockdowns in more than 30 suburbs earlier in the week.
"These numbers are a very real concern to all of us," Victorian Premier Daniel Andrews told a news conference.
The spike in Victoria is being closely watched as the rest of the country has reined in the virus that causes COVID-19.
Australia's most populated state, New South Wales, reported six new coronavirus cases on Saturday, five of them returning travellers from overseas.
The sixth is a past infection and not an active case, according to health officials. The state reported no new cases on Friday.
Overall, Australia has weathered the coronavirus pandemic much better than most other nations, with just over 8,300 cases and 104 deaths so far.