Victoria is bracing for scorching heat, a dramatic cool change and squally winds all in one day.
A statewide total fire ban is in place for Friday, with Melbourne expecting a very hot, sunny day reaching 42C, while in the state's northwest, Bendigo is forecast for 44C and Echuca, Swan Hill, Kerang and Mildura, 46C.
Hot northerly winds coming from inland Australia ahead of a cold front are responsible, the Bureau of Meteorology's Dean Stewart said.
"It's not that often that we get temperatures of that magnitude around 45C, 46C at some locations."
It will be the hottest day in Melbourne since January 13, 2016, Mr Stewart said.
"The good news is it will only be relatively short-lived, that cold front will be coming across Victoria during the day," he added.
The change will reach Melbourne about 4pm and bring a "very sudden" drop in temperature and wind gusts of up to 100km/h.
"We'll go from 42C to the mid-20s within an hour of that change moving through," Mr Stewart said.
Commuters are being warned to brace for changes to services to keep the public transport network moving during the hottest parts of the day, with heat expected to expand rail and tram tracks.
Public Transport Victoria chief executive Jeroen Weimar said there would be a reduction in services, reduced speeds and bottles of water handed out at stations such as Flinders Street.
Acting Premier Tim Pallas urged Victorians to keep a cool head.
"Managing heat, managing fire and also managing safety in the water are going to be critically important issues, people are urged to carry water with them in the hot period of the day," he told reporters.
