Australians across New South Wales and parts of Queensland are bracing for a day of "catastrophic" fire danger which will threaten lives and property.
The NSW Rural Fire Service has warned residents to leave homes immediately, taking pets with them, in areas facing the greatest danger.
The highest level of "catastrophic fire danger" is forecast for the Greater Hunter, Greater Sydney Region and Illawarra/Shoalhaven, while "extreme fire danger" is the warning for the North Coast, Southern Ranges, Central Ranges, New England, Northern Slopes and North Western areas.
"Severe fire danger" is forecast for the Far North Coast, Far South Coast and Monaro Alpine, while a "very high" risk is forecast for the Upper Central West Plains, Lower Central West Plains and Southern Slopes.
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To compound the threat, the Bureau of Meteorology (BOM) is predicting hot, dry and gusty winds on Tuesday followed by a cold front expected to sweep through in the early evening that could see the intense flames quickly change direction.
Weatherzone Meteorologist Ben Domensino said today's dry "southerly buster" will cause any fires burning near the NSW coast to "abruptly change direction".
Rural Fire Service Deputy Commissioner Rob Rogers said: "I've been in this industry for 40 years, and I've not seen a scenario like this before."
"I really haven't — not when you've got all this fire and this catastrophic risk. If someone came to me and said, 'Let's do a scenario role-play' I'd say 'Let's try to keep this a bit more realistic'. It's that sort of out-of-the-box."
Up to 20,000 people are expected to join the firefighting effort today with the Australian Defence Force on standby to help.
Fires in the state's northeast have claimed three lives, destroyed more than 150 homes and razed more than 850,000 hectares of forest and farmland since Friday.
There are 64 fires burning in New South Wales, 40 of which are still uncontained. Premier Gladys Berejiklian declared a state of emergency today, giving emergency powers to Rural Fire Service Commissioner Shane Fitzsimmons and prohibiting fires across the state.
Fire conditions are forecast to be worse today than they were at the peak of the current fire emergency on Friday.
Berejiklian said the last time a state of emergency was declared in New South Wales was 2013 when there were extensive fires in the Blue Mountains west of Sydney.
"The catastrophic weather conditions mean that things can change very quickly," she told reporters in Sydney.
Catastrophic fire danger has been declared for Sydney and the Hunter Valley region to the north today with severe and extreme danger across vast tracts of the rest of the state.
The week-long declaration of a state of emergency gives the Rural Fire Service sweeping powers.
The annual Australian fire season, which peaks during the Southern Hemisphere summer, has started early after an unusually warm and dry winter. The crisis has reignited debate on whether Australia has taken enough action on climate change.
Australia is the world's largest exporter of coal and liquid natural gas. It is also the world's driest continent after Antarctic, which scientist say leaves Australians particularly vulnerable to weather extremes associated with a changing climate.
Carol Sparks, a local mayor who lost her home in a fire near the New South Wales town of Glen Innes, said climate change had contributed to the emergency.
Some residents in the path of dangerous fires blame the intensity of flames on environmentally focused lawmakers who have prevented regular controlled burning of forests to reduce the fuel load in the tinder-dry landscape for fear of smoke and harm to wildlife.
The leader of the minor Australian Greens party, Richard Di Natale, and the party's climate spokesman, Adam Bandt, blamed Prime Minister Scott Morrison's government for the crisis.
"Scott Morrison has not got the climate crisis under control," Bandt said.
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Morrison said Saturday that he had not considered whether the unprecedented fires scorching New South Wales and neighbouring Queensland state were linked to climate change.
"My only thoughts today are with those who have lost their lives and their families. The firefighters who are fighting the fires, the response effort that has to be delivered and how the Commonwealth has to respond in supporting those efforts," Morrison told reporters.
Morrison's deputy Michael McCormack said Monday that now was not the time for political debate on climate change.
"What people need now is a little bit of sensitivity, understanding and real assistance. They need help; they need shelter," McCormack told Australian Broadcasting Corp.
"They don't need the ravings of some pure, enlightened and woke capital city greenies at this time," McCormack said. "What they don't need is Adam Bandt and Richard Di Natale trying to get a political point score on this. It is disgraceful, it is disgusting and I'll call it out every time."
Ken Thompson, who was deputy commissioner of Fire and Rescue in New South Wales until 2011, co-founded the group Emergency Leaders for Climate Action, which includes 23 former senior fire and emergency service leaders from across Australia.
Thompson said he was frustrated that that prime minister had refused to meet with them."Our main concern is with bush fire that our fire seasons are becoming much, much longer that they used to be," Thompson said.
Australian firefighters relied on the same firefighting aircraft that were used to combat wildfires in the Northern Hemisphere fire season, he said.
"Those aircraft come down during our fire season at the end of the North Hemisphere fire season," Thompson said. "The problem is that their fire seasons have become a lot longer as well, so we're being left vulnerable by not having those types of aircraft available to us in Australia at a time when we most need them."
- with AP