Non-drinking water only as fire damages supply

The blaze in Victoria's Otways damaged a local treatment plant in Gellibrand, cutting off clean water.

Water authorities have been carting in water to "top up" the tank after being granted access to the site on Wednesday.

"This water is to connect households and businesses to supply for essential (non-drinking) needs such as flushing toilets and showering," Barwon Water said on Thursday morning.

"We ask that the community only use this water for essential non-drinking purposes and bear in mind that the supply will be contingent on carting (for now)."

Once fire authorities deem it safe for the community to return, Barwon Water plans to set up a temporary supply of drinking water.

An emergency warning for the Carlisle River blaze was downgraded on Wednesday evening after it destroyed three homes and 16 other structures following a wind change in severe heatwave conditions.

But residents of Gellibrand, Barongarook, Carlisle River, Charleys Creek, Kawarren, Lovat and Wimba were told it is still not safe return, with trees and debris blocking roads and creating hazards.

While milder weather is helping firefighters gain the upper hand, Premier Jacinta Allan warned extreme heat was forecast to linger in northern parts of Victoria through to Saturday.

"This summer is far from over," Ms Allan told reporters on Thursday.

"We have many, many weeks of summer ahead of us."

Crews continue to work around the region identifying areas where control lines can be put in during favourable weather conditions.

Forest Fire Management Victoria chief fire officer Chris Hardman said the risk of a flare-up on fire grounds remains.

"There is still a chance that this fire could run again within the next two or three weeks because of the nature of the season," he said.

"It's so dry, you know. If we get some really good rainfall, that will be incredibly helpful, and that will build our confidence."

Six major fires continue to burn across the state, including other out of control blazes at Walwa in Victoria's north and Dargo in Gippsland.

Coastal areas of the state were experiencing cooler conditions on Thursday, with temperatures hovering in the low to mid 20s. 

But there was no respite for inland areas as Albury (41C), Swan Hill (43C) and Mildura (45C) head for highs in the 40s.

Mildura recorded its hottest day on record after the city in the state's northwest hit 48.6C on Tuesday, while nearby towns of Walpeup and Hopetoun posted Victoria's all-time hottest temperatures at 48.9C.

Power was continuing to be restored communities after it was cut to more than 100,000 customers across Victoria on Tuesday night in the record heat.

As of 6pm on Wednesday, 3326 households remained off the grid.

More than 400 homes have been destroyed by fires in Victoria alone this season, with 400,000 hectares of land burnt.