'No homes designed to withstand' coming fire conditions

Tens of thousands of Victorians are on alert for bushfire danger and 100 schools shut as the Australian state braces for potentially catastrophic weather conditions.

The Wimmera region in the west faces a catastrophic fire danger rating on Wednesday, with firefighters coming from interstate to help protect the area.

Five other regions are extreme, with a total fire ban declared for all catastrophic and extreme regions.

Some 30,000 people in communities around two bushfires in the state's west will be sent alerts on Tuesday advising them of the danger and asking them to heed warnings to leave early.

Authorities have created a map of where the fire could potentially go, including towns such as Beaufort, Elmhurst, Amphitheatre, Lexton Learmonth and Clunes.

"Fire, spot fires and ember attack are quite possible in these areas, these could result in loss of homes, closure of roads and isolating communities," Emergency Management Commissioner Rick Nugent told reporters on Tuesday.

Country Fire Authority chief Jason Heffernan said the peak fire threat is expected from midday on Wednesday until about midnight.  He urged people planning to leave the area to get out on Tuesday night or early on Wednesday.

"I would not leave it any later than lunchtime because those weather conditions will become quite nasty from 12 o'clock onwards," he said.

CFA deputy chief Garry Cook said the conditions were all there on Wednesday to encourage bushfires.

"The air mass is really dry, it's got a strong northerly wind pulling all that hot (and) dry air down over Victoria, and then a blustery southwesterly change will come through late in the evening," he told AAP.

"Our job now is to - where we can - prevent anything from starting, and that's (also) the community's job."

Crews were tracking weather conditions hour by hour with the Bureau of Meteorology, Mr Cook said.

He warned Victorians against risking starting fires while the danger was so high, including by operating machinery in vegetation, mowing, welding or grinding.

"Our primary objective is to make sure we don't lose any lives, and the community so far ... have been heeding the warnings," Mr Cook said.

"We've got another really tough day to go and we just ask the community to continue to do their bit."

Victorian premier Jacinta Allan said close to 100 school and early childhood facilities will shut on Wednesday while vulnerable people in aged care and hospitals have been taken away from the danger.

The Mallee region was slated to reach mid-40°C and get winds of up to 45km/h on Wednesday while other parts of the state were also expected to creep into the 40°Cs.

The threat comes as a watch and act alert remains for the wild Bayindeen fire, northwest of Ballarat, which had burned through more than 21,300ha as of Tuesday morning.

So far six homes and 10 other buildings have been lost to the fire.

Crews are coming from New South Wales to help the hundreds of firefighters on the ground who have been battling the blaze since it sparked on Thursday last week. 

Commissioner Nugent said Wednesday's spike day could see the Bayindeen fire run again and head south before swinging back around.

Mr Heffernan warned power could be cut because of fires.

"No homes are designed to withstand those catastrophic conditions. Tomorrow is the day to have a bushfire survival plan."

At the Bayindeen fire, efforts have been on building containment lines.

Crews were working day and night to try to get a consolidated line around the massive blaze but the steep landscape, unfit for fire trucks, has made it difficult to tackle.

There will be 66 aircraft available for Wednesday and NSW is strategically putting aircraft along its side of the border in case fires flare.

Watch and act warnings remain in place for residents of Amphitheatre, Elmhurst, Raglan, Waterloo and other areas, warning locals that it is still unsafe to return.

Three national parks have been shut, including the Grampians National Park which is popular with holidaymakers.