Meteorology said Mildura, a rural city of about 56,000 people, could reach 45 degrees Celsius (113 degrees Fahrenheit). 
"Today is going to be a very challenging day for firefighters," Jason Heffernan of the Victorian fire service told ABC television.
Hundreds of firefighters were still battling a major blaze in Ballarat, 95 kilometers west of Melbourne. The fire, which has been raging since last Thursday, has already destroyed six homes, killed livestock and burned more than 20,000 hectares. 
A heatwave is expected to move in from inland Australia, heading towards Victoria and moving east towards the state of New South Wales.
Heffernan said the current weather pattern could lead to new fires, while strong winds expected Wednesday afternoon could spread the existing fire near Ballarat, urging people to reconsider their decision to stay behind to protect their homes.