Firefighters are desperately trying to control devastating bushfires across NSW before a 'danger day' of weather forecast for Tuesday forcing the Rural Fire Service to issue this dire warning "lives will be at risk".

As the state begins to count the devastating cost of the fires, three people have been confirmed dead and there are fears that number could rise, with more reported missing. More than 150 properties have already been lost to the fires.

While conditions eased today, firefighters are now desperately trying to control the bushfires and the RFS says Tuesday will likely see widespread severe and extreme fire danger from the Queensland border to the south coast and across the central west.

"Tuesday 12 November will be a dangerous day," it tweeted.

"With so many fires already burning, homes and lives will be at risk."

On Sunday morning, 72 fires were burning across NSW, 36 of which were not under control.

Eleven fires remain at a watch and act level.

RFS Inspector Ben Shepherd says fire crews are doing all they can to control blazes already burning before Tuesday.

"We are looking down the barrel of a busy few days and potentially a dangerous day come Tuesday," he told Seven News on Sunday.

"We're trying to get as many of these fires under control before the onset of that weather on Tuesday, but look we won't have these fires under control by that stage we'll have to concentrate where it is burning close to residential areas."

NSW Rural Fire Service fire behaviour analyst Simon Heemstra described the upcoming conditions as "very hot, very dry and very windy".

"The three are lining up on Tuesday for potentially significant fire weather," he said.

In the meantime RFS Commissioner Shane Fitzsimmons says assessment teams are bracing themselves for "considerable losses".

"There are communities and fire grounds where we are expecting to tally up considerable losses of homes and other properties," he said.

"A number of our own fire stations have been destroyed." At least 150 homes have been destroyed by the fires although this number is likely to climb as detailed assessments begin.

Mr Fitzsimmons said other important community assets had also been lost in the fires.

"We're talking about schools being destroyed, we're talking about community halls, bridges, power poles," he said.

"All of those sorts of things - they get consumed in the path of a volatile fast-moving fire."

Fire assessment teams would comb through devastated areas over the coming days, Mr Fitzsimmons said.

"The more forensic process of getting in and doing the detailed assessments will come over coming days.

"Clearly, from what we are seeing, and we do not have indicative assessments from all these fire grounds yet, but estimates are at least 150."

NSW Premier Gladys Berejiklian said South Australia, Tasmania and Victoria were all sending reinforcements to help the state fight fires.

The premier on Sunday said the federal and state governments had already moved to put disaster relief arrangements in place.

"I want to assure communities throughout the mid and north coast no matter in which way they've been impacted, we know for some people they've lost everything, for some people they've lost a loved one ... no matter what anyone's circumstances please know we're here to support you," Ms Berejiklian told Seven News.

An estimated 2000 people have used the more than 15 formal evacuation centres set up.