A total fire ban has been declared for the entire state of Victoria as the Bureau of Meteorology (BOM) predicts hot, dry weather.
Melbourne and Geelong face a day of extreme fire danger as does the southwestern region and the Wimmera with temperatures expected to hit 44C.
A severe fire danger warning is in place for the rest of the state.
Bureau of Meteorology duty meteorologist Dean Sgarbossa said there was no respite from the heat on Thursday night with the mercury failing to dip below 20C.
By 8am (AEDT) on Friday, the temperature in Melbourne had nearly reached 30C and the bureau expects it to soar quickly until a cool change brings some relief in the evening.
However, Mr Sgarbossa warns the change won't reach all parts of the state.
'Tomorrow we're still expecting high temperatures, up to the low 40s in the north.'
Acting Premier Peter Ryan has urged all Victorians to ensure they are prepared and have fire plans in place.
'We are at the brink of our sternest test for the year 12/13 bushfire season,' he said on Thursday.
Mr Ryan said if people in regional areas were unsure whether to stay or to go, they should go.
'Don't think about it until it is too late,' Mr Ryan said.
Country Fire Authority chief officer Euan Ferguson also warned that 'waiting and seeing' could prove to be a fatal mistake because on a bad day, such as today, fires can travel extremely quickly.
'Smoke on the horizon can be a fire on your doorstep in minutes,' he said.
Fire Services Commissioner Craig Lapsley said Friday would be a key focus for firefighting agencies ahead of a string of hot, dry days.
Towns in the Mallee will bake in forecasted temperatures of 44C for Mildura, Walpeup and Ouyen.
Horsham in the Wimmera faces hot gusty winds and temperatures up to 43C.