In Victoria's LaTrobe Valley, fears were held for coal mines and the power stations that supply 85 per cent of the state's electricity, although there appeared to be no immediate threat late yesterday.
As more than 1000 firefighters prepared to battle huge fronts through the night, state Fire Service Commissioner Craig Lapsley warned that yesterday was Victoria's most dangerous since the 2009 Black Saturday disaster.
In the past two days Victorian crews have battled 150 fires, 37 of which were still burning late yesterday.
With total fire bans covering SA and Victoria, the return to heatwave conditions in the past few days compounded the danger of scrub and bush dehydrated into explosive tinder, and increased the threat from fires that have burned for days, or even weeks.
Victoria mobilised its entire emergency resources, topping up rural fire services with brigades from metropolitan Melbourne and crews from state parks and the Department of Environment and Primary Industries.
Their battle deepened as fires driven by northerly winds suddenly switched direction ahead of a cooler southerly change which, despite almost immediately cutting temperatures by 10C, brought no immediate relief.
A similar crisis faced SA, which pressed all available firefighters into action as a fire near Bangor in the Southern Flinders Ranges, alight for more than three weeks, raged out of control, threatening life and property. There are unconfirmed reports of properties being destroyed.
Hopes were pinned on forecasts of winds moderating overnight and temperatures falling to 20C or less.
The most worrying of the 11 fires rated as emergencies for Victorian brigades were burning in heavily populated fringes of Melbourne.
Homes are known to have been lost around Gisborne, about 55km northwest of Melbourne. Fires were also close to Mickleham, a suburb just 30km north of the CBD, and Warrandyte, about 25km to the northeast.
Homes were confirmed lost at Mickleham, Gisborne and Warrandyte. A winery was also burned.
ABC reporter Karen Percy said residents of Warrandyte fled after spot fires broke out in a nearby paddock and explosions were heard. One family of five left just 30 minutes before flames engulfed their home.
Late yesterday major fires were also out of control in Gippsland, the huge rural region north from Melbourne to the NSW border which was devastated in the Black Saturday conflagration.
Flames were threatening properties and communities stretching from Morewell, in the LaTrobe Valley 50km east of Melbourne, to Yarrum in the southeast, and in East Gippsland around Orbost and Buchan.
Late yesterday Orbost residents were told to seek shelter in the town's centre, and others near Goongerah, also in Gippsland, were urged to leave.
In SA hundreds of firefighters were battling a number of serious outbreaks, the worst the huge fire near Bangor which erupted again after burning for 25 days.
Homes and properties are said to have been destroyed in a battle that raged there all Saturday night and was continuing as dusk fell yesterday.
Patients were evacuated from a Bangor Hospital and emergency warnings were in force for communities including Beetaloo, Laura, Stone Hutt, Wirrabara and a nearby forest.
SA Country Fire Service co-ordinator Brenton Eden told reporters yesterday there was no hope of bringing the fire under control for days. "What is typical in that area is that fire will remain a concern to us until we get significant rain over the fire ground."
