Residents and holidaymakers in Grampians National Park have been told to evacuate immediately because of two raging bushfires.
Emergency warnings have been issued on Tuesday for out-of-control blazes at Bellfield and Mt Stapylton.
The orders to leave immediately apply to those in Halls Gap, Bellfield, Bellfield Settlement, Lake Fyans, Pomonal, Dadswells Bridge, Ledcourt, Roses Gap and Wartook.
"Leaving immediately is the safest option, before conditions become too dangerous," alerts from the Vic Emergency website said.
"Emergency services may not be able to help you if you decide to stay."
The Mt Stapylton fire is set to head towards Dadswells Bridge and Ledcourt but conditions are "dangerous and unpredictable," the emergency website stated.
People affected by that fire have been told to head towards Stawell, with authorities warning the Western Highway is closed between Horsham and the Warracknabeal-Stawell Road intersection.
The Bellfield blaze is travelling in a southerly direction towards Pomonal, with people affected by that blaze being told to go towards Ararat using Ararat Halls Gap Road.
Some 38 schools and 17 early childhood centres have shut as conditions forecast include winds of up to 100km/h, possible dry lightning and thunderstorms.
A catastrophic fire danger rating has been declared for the Wimmera region, extreme fire danger forecast for the Mallee, a high danger rating for the rest of the state except for East Gippsland and a total fire ban in much of the state.
Country Fire Authority chief officer Jason Heffernan said it would be some of the most dangerous grassfire conditions since the Black Summer of 2019-20.
Black Summer was one of the most intense and catastrophic fire seasons on record in Australia.
Power providers have crews on standby to respond to any outages caused by damage to poles and wires, Energy Minister Lily D'Ambrosio told reporters.
Tasmania, South Australia and Western Australia are also on alert for extreme fire danger amid heatwave conditions.
Tasmania Fire Service deputy chief officer Matt Lowe said current weather conditions combined with a dry landscape meant fires could spread easily and become difficult to control.
"TFS are putting a temporary hold on issuing fire permits in the south and north of the state until 2am Thursday," he said on Monday.
"While we are not declaring a Total Fire Ban, we are asking people to think carefully before lighting campfires and using machinery, and if doing so please be extremely cautious."
South Australians are bracing for a hot and dry Tuesday and extreme fire conditions.
Total fire bans have been declared, with extreme fire danger ratings for mid north, Riverland and Murraylands.
The South Australian Country Fire Service says "very hazardous" fire weather conditions are predicted.
The Bureau of Meteorology has also issued a heatwave warning for parts of Victoria, with conditions expected to ease with a cooler change from late Tuesday night through early Wednesday morning.
A severe heatwave warning is also in place for parts of Western Australia including Kimberley, Gascoyne, Central West and Great Southern Districts.
Australian Associated Press