Victoria state, where the so-called Black Saturday firestorm flattened entire villages in 2009 and destroyed more than 2,000 homes, was again bracing for extreme fire weather.
"These next four days promise to be amongst the most significant that we have faced in Victoria since Black Saturday," said acting state premier Peter Ryan.
Tens of thousands of firefighters were on standby, and 1,290 brigades were in a "state of high preparedness", he added, with the peak danger day expected on Friday when very strong winds are forecast.
A grass-fire tested crews early at Little River west of Melbourne, racing out of control and triggering a brief emergency alert before water-bombing aircraft managed to bring it under control.
Victoria and neighbouring South Australia state are bracing this week for what forecasters are describing as a "severe to extreme heatwave conditions", with successive days of temperatures above 40 degrees Celsius expected.
A similar heatwave struck before the 2009 fires, Australia's worst natural disaster of the modern era in terms of casualties. An estimated 374 people died during the preceding heatwave, with another 173 fatalities in the firestorm itself.
Today, players at the Australian Open were sweltering.
A ball boy collapsed and water bottles melted on court as the mercury soared above 40 degrees Celsius.
Experts said the outlook had echoes of 2009.
"The forecast weather patterns are quite reminiscent of conditions before Black Saturday, with severe and expansive high temperatures across the southern part of the continent and the presence of low pressure cells on either side of the country in the tropics," said bushfire specialist Jason Sharples from the University of New South Wales in Canberra.
