One person died in the Grampians bushland in the south-eastern state of Victoria, about 186 miles west of Melbourne, where bushfires are burning out of control amid temperatures that have hit above 40 degrees Celsius (104 degrees F), destroying or damaging houses.
Victoria was the hardest hit, with 70 bushfires burning out of control. Dozens of blazes are burning in South Australia, Western Australia and New South Wales.
Authorities have issued seven emergency warnings to severely affected areas, prompting hundreds of residents to leave their homes.
Victoria Fire Services Commissioner Craig Lapsley said conditions were "up there" as the worst since the fires that killed 173 people in 2009.
Mr Lapsley said the fire in the Grampians bushland was so intense it had "created its own weather", triggering lightning and spot fires. He said strong wind changes and thunderstorms forecast for last night could exacerbate conditions.
A Victoria Country Fire Authority spokeswoman said: "There is a stronger wind expected to come through there and that could create worse conditions."