Thousands of Victorians have been told to leave their homes as the state braces for catastrophic bushfire conditions.
Residents in communities surrounding the Bayindeen bushfire, northwest of Ballarat, are being sent mobile phone alerts on Tuesday advising them to leave their homes early.
Forecast temperatures in the high 30Cs and wind gusts up to 80km/h in the area on Wednesday are expected to fan the fire.
Authorities have created a map of where the fire could go, including towns such as Beaufort, Elmhurst, Amphitheatre, Lexton, Learmonth and Clunes.
"Fire, spot fires and ember attack are quite possible in these areas," Emergency Management Commissioner Rick Nugent told reporters.
"These could result in loss of homes, closure of roads and isolating communities."
Relief centres remain open in Ararat and Maryborough.
A catastrophic fire danger rating has been declared for the neighbouring Wimmera region in the state's west.
"If any fires do get going, they will be uncontrollable and uncontainable," Bureau of Meteorology meteorologist Dean Narramore warned.
Five more regions are facing extreme danger and total fire bans have been declared.
Mr Nugent said those living close to bushland, rural grass and paddocks in catastrophic or extreme-rated regions should similarly flee no later than midday Wednesday, when the peak fire threat is expected to begin.
"You can go to regional cities or you can go to Melbourne to stay with family and friends but please if you're in a bushfire-risk area, please leave and leave early."
Extreme fire danger is also forecast for much of eastern South Australia after temperatures in the state reached the 40Cs on Tuesday.
Victoria's Country Fire Authority chief Jason Heffernan warned fires could cut power and encouraged residents to carry a transistor radio with batteries to keep up to date with emergency updates.
"No homes are designed to withstand those catastrophic conditions," he said.
"Tomorrow is the day that you must have a bushfire survival plan."
Victorian Premier Jacinta Allan said almost 100 school and early childhood facilities will shut, while vulnerable people in aged care and hospitals have been taken away from the danger.
Northwestern parts of the state are tipped to record temperatures in the mid-40Cs and be buffeted by winds of up to 45km/h on Wednesday.
Central and northern areas are expected to sweat through temperatures in the high 30Cs and dry lightning is forecast to move through large parts of the state, potentially sparking more fires.
A watch and act alert remains for the Bayindeen fire, which had burned through more than 21,300 hectares as of Tuesday morning.
Six homes and 10 other buildings have been lost to the fire so far.
More than 110 NSW firefighters are coming to help crews battling the blaze since it was sparked on Thursday.
Firefighters have been working to get a consolidated line around the massive blaze but the steep landscape, unfit for fire trucks, has made it difficult to tackle.
Mr Nugent said Wednesday's heat spike could see the Bayindeen fire run outside containment lines and head south before swinging back around.
There will be 66 aircraft available for Wednesday and NSW is strategically putting aircraft along its side of the border in case fires flare.
The Grampians National Park, near where 46 homes were lost in separate fires a fortnight ago, is among three parks that will be closed.
Ms Allan said arrangements were in place to move inmates from the minimum security Langi Kal Kal prison in Trawalla, 40km west of Ballarat, to the Western Plains Correctional Centre at Lara.
