A wind change that will cool down long-suffering Victorians could also create havoc for several bushfires burning around the state.
Fire Services Commissioner Craig Lapsley said predictions for Friday of 40C-plus temperatures, strong winds and a late gusty change made for some of the state's worst conditions since 2009.
"It's certainly up there - the fact that we've had a pre-run of three, four days of this sort of weather," he told reporters.
"A gusty change sees fires potentially change in size and threaten different communities."
A total fire ban has been declared for the entire state on Friday.
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A major bushfire burning near in the Grampians, in the state's northwest, sparked emergency warnings for surrounding towns on Thursday, and is expected to continue to pose a threat on Friday.
Visitors were told to leave the popular tourist area on Thursday as two out-of-control bushfires merged to form a 1,500-hectare blaze.
Mr Lapsley said the fire had increased in intensity and would remain out of control until Friday.
"That will be a going fire on Friday when the temperatures are high and the wind speeds from the southwest will be at their height," he said.
"That's a fire that has significant potential."
Around the state, crews were kept busy by 1000 new incidents on Thursday, the majority of which were small fires sparked by lightning strikes.
Emergency warnings were also issued on Thursday for fires at Trafalgar, in the state's east, Tempy, in the state's northwest, and Telopea Downs on the South Australian border.
The warnings for Trafalgar and Tempy were downgraded but residents were urged to remain vigilant.
Mr Lapsley said the fire danger, while severe, would not be at the catastrophic level experienced on Black Saturday in February 2009, when fires killed 173 people and destroyed more than 2000 homes.
Emergency Services Minister Kim Wells said everyone in Victoria needed to have a fire plan and leave early if necessary.
"No matter where you live, it's up to you to understand your fire risk," he said.
"If the fire danger rating is severe, extreme or code red, you are risking your life and your family's life if you wait and see.
"The message is clear - leave and live."
While Melbourne and the state's south will enjoy cooler weather over the weekend, Mr Lapsley warned the cool change won't go through the northeast until later on Saturday.
