Hundreds of schools were closed and residents were urged to evacuate woodlands for the relative safety of city centres Tuesday as hot, dry and windy weather posed an extreme fire danger across Australia's most populous state.

New South Wales is under a week-long state of emergency, a declaration that gives the Rural Fire Service sweeping powers to control resources and direct other government agencies in its efforts to battle fires.

The worst fires are expected in the state's northeast, where three people have died and more than 150 homes have been destroyed since Friday, as well as around Sydney, Australia's largest city.

Rural Fire Service commissioner Shane Fitzsimmons said 3,000 firefighters were available to fight more than 50 fires blazing across the state. The fires are expected to worsen as winds are forecast to gust at between 70 km/h and 90 km/h later Tuesday.

"Now is the time to exercise those decisions to leave, leave early and go to safer locations, safer towns and villages or safer places in your local community, such as the shopping centres," Fitzsimmons told reporters Tuesday.

"We plan for these sorts of days. But we always hope they never come," he added.

More than 600 schools and technical colleges across the state are closed on Tuesday because they are close to woodlands at risk of fire.

Fire season started early

The annual Australian fire season, which peaks during the Southern Hemisphere summer, has started early after an unusually warm and dry winter.

More than one million hectares of forest and farmland has already burned across the state this fire season, more than three times the area that burned during the entire last season, Fitzsimmons said.

Damage caused by a bushfire is seen at resident Brian Williams's resort in the Australian state of Queensland on Monday. (Rob Maccoll/AAP/The Associated Press)

Premier Gladys 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 Monday in Sydney.

Catastrophic fire danger was declared for Sydney and the Hunter Valley region to the north on Tuesday with severe and extreme danger across vast tracts of the rest of the state.

New South Wales state Emergency Services Minister David Elliott said residents were facing what "could be the most dangerous bush fire week this nation has ever seen."

Doctors and paramedics have treated more than 100 people for fire-related injuries, including 20 firefighters, Ambulance Commissioner Dominic Morgan said Monday.

North of New South Wales, wildfires destroyed nine homes in Queensland state, where air quality plummeted in Brisbane, the state capital, and surrounding cities.

The crisis has reignited a debate on whether Australia has taken enough action on climate change.

Trees are burned black after a wildfire in Old Bar. (Peter Parks/AFP via Getty Images)

Australia is the world's largest exporter of coal and liquid natural gas. It is also the world's driest continent after Antarctica, which scientists 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.

Igniting a blame game

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 spokesperson, Adam Bandt, blamed Prime Minister Scott Morrison's government for the crisis.

Fire burns on Bolivia Hill near Glen Innes on Sunday. (Brook Mitchell/Getty Images)

"Scott Morrison has not got the climate crisis under control," Bandt said.

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.

PM's deputy slams 'woke capital city greenies'

"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.

A sign on a fire station in Taree, 350 kilometres north of Sydney, warns of 'catastrophic' fire conditions. (Peter Parks/AFP via Getty Images)

"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."

Waiting on equipment

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 the prime minister had refused to meet with them.

"Our main concern is with bush fire that our fire seasons are becoming much, much longer than 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."