It is the first time the area has experienced the classification since ratings were standardised across the country a decade ago, following the Black Saturday fires in Victoria.
Researchers claim the fires are happening for a number of reasons - most of which can be linked to climate change.
What does the science say?
The overwhelming scientific consensus is that Australia's fire season is growing longer and more intense due to the effects of climate change.
The Bureau of Meteorology (BOM) stated in a report last year that Australia's climate has warmed just over 1°C since 1910.
The report said climate change has seen an increase in extreme heat events and increased the severity of natural disasters, such as drought.
"There has been a long-term increase in extreme fire weather and in the length of the fire season across large parts of Australia since the 1950s ... Climate change, including increasing temperatures, is contributing to these changes," it said.
Professor Glenda Wardle, a professor of ecology and evolution at the University of Sydney, said climate change is “causally linked to the health of the bush” and has “both direct and indirect pathways of causation to catastrophic fires”.
"Much of NSW is also in drought and trees are dying and fuel loads are very dry, leading to dangerous conditions for fires to burn more intensely and spread fast,” she said.
"Under climate change, droughts are going to get longer and come more often, increasing the impact of fires.
"The place to take action is at the start of this causal chain – do not extract coal, reduce CO2 emissions, and plan to share water more carefully to keep our bush healthy and to provide towns with drinking water.”
What makes a bushfire?
Ross Bradstock, director of the Centre for Environmental Management of Bushfires at the University of Wollongong, said bushfires require four key ingredients, each of which can be linked to climate change.
"You need ... a continuous layer of fuel across the landscape," Professor Bradstock said.
"The second ingredient is that fuel has to be dry and the third is hot, windy, low humidity weather - because once you have got a fire going, that makes it spread faster.
"Finally, you've got ignitions - either coming from people or natural sources, like lightning."
Professor Bradstock said that "there is recently-published evidence the dry winters we have been having and the increasingly early starts of the fire season is directly linked to climate change".
"Yes, it is difficult to specifically say this particular event on this day is due to climate change - but the evidence around that is strong."
Are hazard reduction restrictions to blame?
Some in the federal government have attributed the increased risk on newly-imposed restrictions on hazard reduction burning - low-intensity burns to remove vegetation so bush or grass fires are less intense.
It is different to backburning, which specifically refers to the starting of small, controlled fires in the path of a bushfire to reduce the amount of fuel available.
But David Bowman, director of the Fire Centre Research Hub at the University of Tasmania, said restrictions on hazard reductions are not entirely to blame.
"At the very core, we have a climate signal. There's extreme drought, extreme fire weather conditions - fire weather that you would expect in summer, not in spring,” he told the ABC on Monday.
"Yes, there is a role for managing fuels with hazard reduction burning - but would hazard reduction burning programs on their own stem this fire crisis? No, absolutely not."
What can we expect now?
The BOM said 2017 and 2018 were Australia's third and fourth-hottest years on record.
In April, a group 23 former fire chiefs warned climate change is worsening extreme weather and putting people in danger.
In September, the Bushfire and Natural Hazards Cooperative Research Centre (BNHCRC) released its annual seasonal bushfire outlook, describing the east coast of Australia as having "above normal fire potential".
"What all the evidence is showing us (is) that the temperature is sitting about one degree above long-term averages. That is leading to a much earlier start fire season around the world. That is internationally noted,” BNHCRC CEO Richard Thornton said.
"We are also seeing the cumulative amount of fire danger during a fire season going up - the time between these really extreme fire years will get shorter and shorter and shorter.
"We will see these conditions come around more frequently."
Can we curb climate change?
Last year, a United Nations report said Australia was falling short in efforts to cut its carbon emissions.
That "may, in some cases, reflect relatively low ambition", the report said.
The Australian government says it is meeting its emissions reduction targets.
On Monday, Natural Disaster and Emergency Management Minister David Littleproud talked up Australia's climate change action.
He said Australia is "leading the world [on climate change], but we need the world to lead with us".
"We have made our commitments globally and we need other international communities to come with us," he said.
Given the way things are going, the organisation of firefighting resources might need reform in the future, Dr Thornton said.
"Our resource sharing arrangement works okay at the moment,” he said.
"But as we look into a future where fire seasons are getting longer and there starts to be overlaps between fire seasons in Australia and the northern hemisphere, who we share resourcing with, we're a bit more uncertain."