AUTHORITIES have warned of extreme fire weather in Victoria tomorrow as blazes destroy homes and cut off power in South Australia.

An extreme fire danger has been issued for northern Victoria and east Gippsland tomorrow with high temperatures and strong winds forecast.

Department for Sustainability and the Environment state duty officer Dennis Ward says it is important people travelling anywhere over the Christmas period stay informed and alert.

"We are asking all Victorians to be aware of the safety issues and include any holidays or travel in their bushfire survival plans,'' Mr Ward said.

"This means planning ahead, checking on conditions, tuning in to the emergency broadcasters and seeking out information before visiting.''

Senior forecaster Phil King at the Bureau of Meteorology says today's temperatures hit 40 degrees in Victoria's west, and the hot weather front is moving slowly across the state.

An "extremely dangerous" fire has destroyed at least five houses on the outskirts of Port Lincoln and has cut power across the city, plunging it into chaos, AdelaideNow reports.

The fire has burnt through main electricity lines, blacking out at least 6000 properties. It also has destroyed a shed and damaged the Port Lincoln SES headquarters.

There are unconfirmed reports that several homes have been lost while roads near the fire are bottle-necked with people trying to flee its path.

Meanwhile, the CFS says an extremely dangerous bushfire is burning out of control at Ninga Ninga, near Taratap, in the Lower South East . The fire is about 50km north of Kingston.

The CFS also says a bushfire on Donovans Rd, near Wye, 20km south east of Mt Gambier near the Victorian border, is travelling in a south-easterly direction towards Piccaninnie Ponds, although its threat has been reduced.

The CFS advises that leaving fire areas now may be the safest option for residents who don't have a bushfire survival plan.

Read more at AdelaideNow