NSW Premier Gladys Berejiklian has declared a state of emergency ahead of tomorrow's "catastrophic" conditions as bushfires continue to rage in the region.

She took that step in response to a request from RFS Commissioner Shane Fitzsimmons last night.

"Our state has already been hit by some of the most devastating bushfires we have ever seen, with three lives lost and more than 150 structures destroyed," Berejiklian said.

"With catastrophic weather conditions predicted for this week, particularly Tuesday with hot weather and strong winds, I have decided to take the Commissioner's advice and make this declaration.

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Firefighters hold back a fire threatening a house at Tinonee near Taree on the NSW mid north coast. Photo / News Corp Australia
Firefighters hold back a fire threatening a house at Tinonee near Taree on the NSW mid north coast. Photo / News Corp Australia

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"It will ensure the state is best placed to respond to the predicted fire conditions."

She pointed out that this is the first time since new fire danger ratings were introduced in 2009 that a catastrophic rating has been forecast for Sydney.

The last state of emergency in NSW was back in October of 2013. In effect, the measure transfers powers from the state government to the RFS Commissioner.

Fitzsimmons will have the power to directly control and coordinate the allocation of government resources, close roads and thoroughfares to traffic, pull down or shore up infrastructure, and enter or take possession of property.

The declaration is valid for a period of seven days, starting today.

Firefighters are battling to contain more than 60 bushfires still raging across New South Wales and Queensland before "catastrophic" weather conditions hit tomorrow.

Three people have died and 200 homes and sheds have been lost to the fires so far. Forty blazes remain out of control and a total fire ban is in effect.

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Experts are warning the worst is yet to come, with high winds, dry air and temperatures in the high thirties forecast to combine dangerously on Tuesday.

Anthony Clark from the Rural Fire Service said the situation would be "as bad as it gets".

"There's a lot of hard work ahead of us, but the simple message is we're not going to get on top of those fires before these really bad conditions hit on Tuesday," Clark said.

Meteorologist Ben Domensino said a mass of hot air was moving across to the east from Western Australia.

"It is elevating fire danger ratings in South Australia and parts of Victoria today on Monday, then on Tuesday, the threat will shift and focus into NSW and Wednesday, it pushes further north," he said.

Bruce Annetts is a volunteer with the NSW Rural Fire Service. Photo / News.com.au
Bruce Annetts is a volunteer with the NSW Rural Fire Service. Photo / News.com.au

"So that's why we're seeing these danger ratings in South Australia elevated fire danger ratings across multiple states on multiple days.

"The drought's been widespread and in some places record breaking.

"We have known this has been coming for months because we've had this dry weather leading up to the hottest time of year.

"Now we're seeing the winds increasing, the temperatures increasing, which are typical of this time of year. But we don't normally have this much fuel."

The conditions are expected to greatly expand the area at risk from "extreme" fire danger. On Tuesday the Hunter, Illawarra and greater Sydney regions in NSW will face that danger. For Queensland, the threat will persist into the following days as well.

There are also fears for residents in parts of Western Australia, with an extreme fire danger forecast for the South Interior.