Bushfires raged out of control across Australia's most populous state Tuesday, fanned by intense heat and high winds in "catastrophic" conditions that targeted homes and triggered evacuations.

More than 140 fires were burning across New South Wales state late in the day, around 40 of them uncontained, state Rural Fire Service commissioner Shane Fitzsimmons told reporters in Sydney.

"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, which claimed 173 lives, 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, with blustery winds and temperatures reaching 45 degrees Celsius (113 degrees Fahrenheit) in parts of the state, although the heat dropped as night fell.

So far there were reports of just one home being destroyed in the state, at Jugiong near the Australian Capital Territory border. Another two homes were razed in central Victoria state, local media said.

Fitzsimmons said fire crews faced a long night.

"We've still got many hours of very difficult conditions being faced for NSW. That's tonight alone, let alone looking into tomorrow," he told ABC television.

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

Shoalhaven mayor Joanna Gash said the area was a "tinderbox".

"Things are not looking real good," she told Sky News.

Also in southern New South Wales, authorities were battling an out-of-control grass fire encroaching on properties in Brogo, about 160 kilometres (100 miles) south of the national capital Canberra.

"We just looked at each other and said 'We're leaving'," Brogo resident Hallie Fernandez-Markov told AFP from the town of Cobargo, where she was staying with friends after fleeing her guest house.

The popular tourist resort of Kings Canyon south of Alice Springs was in danger after a blaze spread from the Watarrka National Park, with visitors evacuated by road shortly before the fire hit.

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

Temperatures soared so high, and are expected to continue climbing in the days ahead, that the Bureau of Meteorology was forced to add new colours -- deep purple and pink -- to its charts for forecasts above the previous limit of 50 degrees.

Fitzsimmons said while cooler weather had begun to sweep in from the south, seeing temperatures in some areas plummet from 40 degrees to 24 in minutes, the front was moving slowly.

There were also extreme conditions in the state of Victoria, with the Australian Associated Press citing witnesses as saying two homes were destroyed and two people injured in a bushfire near the town of Snake Valley.

"We have lost a couple of homes," one man, who did not want to be named, said.

Wildfires destroyed more than 100 homes in Tasmania over the weekend, and around 40 blazes were still burning across the southern island state but the immediate threat to homes was believed to have passed.

Tasmanian police, who Tuesday continued searching burned out properties, said no bodies had been discovered so far.

Initial reports said as many as 100 people could be missing, but police said there was confusion about movements during the crisis and there were only "a handful" of people they were trying to locate quickly.

Fires are a regular occurrence in vast and arid Australia, particularly between December and February.

The last four months of 2012 were abnormally hot and the warm conditions have been exacerbated by very dry conditions due to the delayed start to a weak monsoon.