Victorians have been urged to prepare for scorching heat, potentially deadly conditions and an extreme risk of fires as dry, hot weather sweeps across the state.
Melbourne is set to hit 42C on Friday, while in the state's northwest, Bendigo is forecast to reach 44C and Echuca, Swan Hill, Kerang and Mildura, 46C.
A dramatic cool change will provide welcome relief for some areas later in the day, but is likely to bring gusts of up to 100 km/h which could exacerbate fires.
Thunderstorms are also expected in parts of central and eastern Victoria in the late afternoon, with the possibility of dry lightning strikes posing a risk of fire.
A statewide total fire ban is in place and extreme fire warnings have been issued for Mallee and Wimmera.
"If a fire starts it's going to be uncontrollable, it's going to be fast-moving," Emergency Management Commissioner Andrew Crisp said.
"So this is a timely reminder for people, if you have not done your preparation and planning in relation to fire, then you better get on to it."
Hot air from central Australia is advancing through Victoria, delivering the rising temperatures.
The Bureau of Meteorology's Kevin Parkyn said the weather "has all the ingredients that make fires difficult to control".
"It's hot, the air mass is particularly dry, we've got north to northwesterly winds that are quite gusty, that fan fires in the landscape," he told reporters.
"And probably the other element that makes the day more dangerous than it would be otherwise is a wind change."
The change will reach Melbourne between 3pm and 4pm, bringing a sudden drop in temperature to as low as the mid-20s, and wind gusts of up to 100 km/h.
Steve Warrington, Country Fire Authority chief officer, described the wind change as a "killer", and urged campers and holiday-makers to prepare for the dangerous conditions.
"Our advice would be don't get on the road at that particular time and even consider delaying your return home from holidays or being on the road at all at that particular time," he said.
The health of vulnerable people is also at risk as the temperatures soar on Friday.
Parents have been reminded to keep young children out of cars, with just a matter of minutes needed to render them unconscious on a hot day.
Victoria's acting Chief Health Officer Brett Sutton said the hot conditions could prove deadly for some.
"There will be scores of people who have cardiac arrest or who present in a really severe state by ambulance," he said.
Commuters are being warned there may be 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.
