SE Australia braces for 'catastrophic' fires with temperatures set to top 50C

Firefighters battling scores of bushfires across southeastern Australia face more extreme heat in coming days as "catastrophic" conditions targeted homes and forced evacuations.

The heat has even prompted the weather bureau to upgrade its temperature scale with new colours on the climate map to reflect new highs forecast to hit 50 degrees Celsius next week.

More than 130 fires were burning across New South Wales state yesterday, 40 of them uncontained, state Rural Fire Service commissioner Shane Fitzsimmons said.

"You don't get conditions worse than this - we are at the catastrophic level," he said.

Introduced after the 2009 Black Saturday firestorm in Victoria state that killed 173, a "catastrophic" rating means fires will be uncontrollable, unpredictable and fast-moving, with evacuation the only safe option.

New South Wales faced one of the highest-risk fire days in its history, fanned by high winds and temperatures reaching 45 degrees in parts of the state.

While no deaths had been reported, officials remained on alert, with particular concerns about the Shoalhaven, Illawarra and Southern Ranges region south of Sydney, all popular summer holiday locations.

Shoalhaven mayor Joanna Gash said the area was a "tinderbox", and the extreme conditions were unprecedented.

In New South Wales, authorities warned that an out-of-control grass fire was encroaching on properties at Brogo, about 160 kilometres south of Canberra.

"Aussie wildfires could have killed at least 100", video by AFP

Much of southern Australia is enduring a summer heatwave and a total fire ban is in place throughout New South Wales, while all national parks are closed, with temperatures topping 42 degrees in Sydney and 45 in the state's west.

Temperatures have soared so high, and are expected to continue climbing, that Central Australia was shown with a purple area on the latest Bureau of Meteorology forecast map issued for next Monday.

The new colour, which also features a pink code for temperatures from 52 to 54 degrees, reflected the potential for old heat records to be smashed. Australia's all-time record temperature is 50.7 degrees, set in January 1960 at Oodnadatta in the state of South Australia

There were also extreme conditions in Victoria, while a bout 40 blazes were still burning across the southern island state but the immediate threat to homes was believed to have passed.

As Tasmanian police continued searching burned out properties for bodies, one family's terrifying ordeal was captured on video. It shows a woman and her five grandchildren wading into the sea as bushfires ravaged their nearby home in Dunalley. The children's grandfather, who shot the video, risked his life to grab a dinghy off the foreshore, loaded the children and his wife and dragged them along the shore to safety.