Total fire bans have been declared and firefighters are coming from interstate as Victoria braces for potentially catastrophic weather conditions.

The Wimmera region is facing a catastrophic fire danger rating for Wednesday and five other regions are extreme.

A total fire ban has been listed for all catastrophic and extreme regions.

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

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

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

Crews are coming from NSW to help the hundreds of firefighters on the ground who have been battling the blaze since it sparked on Thursday.

“Tomorrow will be a significant and challenging day for the emergency services across the state,” Emergency Management Comissioner Rick Nugent told reporters.

He said Wednesday’s spike day could see the Bayindeen fire run again and head south before swinging back around, and those in surrounding areas should pre-emptively leave their homes.

“No homes are designed to withstand those catastrophic conditions,” CFA chief officer Jason Heffernan said.

“Tomorrow is the day to have a bushfire survival plan.”

Heffernan warned power could be cut because of fires.

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.

– AAP