'Too big to put out': Mega fire near Sydney will burn for 'many weeks'

The "mega fire" raging near Sydney's northwestern outskirts is going to take "many weeks" to put out, the NSW Rural Fire Service says.

Firefighters are concerned the Gospers Mountain blaze, which has merged with neighbouring fires, could start burning towards Gosford.

"The total area burnt by these fires is around 335,000 hectares," the RFS said in a statement.

"These will take many weeks to put out - and only when we get good rain."

The Gospers Mountain fire in the Wollemi National Park alone has burnt over 280,000 hectares.

Firefighters work to protect a property on Kyola Road in Kulnura as the Wrights Creek fire approaches Mangrove Mountain north of Sydney. Source: AAP/Dan Himbrechts

Hawkesbury City Council deputy mayor Mary Lyons-Buckett said the blazes can only be described as a "mega fire".

Evacuation centres have been set up at the Cessnock and Wyong Rugby League clubs and Gosford RSL.

On Saturday morning, there were 94 bush fires across the state including 11 at a "watch and act" level.

The Illawarra-Shoalhaven region has also been placed on a total ban, joining most of the east of the state.

Bans were already in place for eight regions including greater Sydney and Hunter as well as most of the state's north.

Firefighters will have a brief window over the weekend to get on top of the crisis before the weather deteriorates early next week.

Pedestrians wear masks as they walk towards Sydney's CBD as smoke haze blankets the city. Source: AAP/Paul Braven

The Bureau of Meteorology has painted a grim picture for the coming week, with winds forecast to whip dangerous fire grounds and no rain relief in sight.

Some fires are generating plumes of smoke that are so vast, they appear as rain on the bureau's rain radar.

"The massive NSW fires are in some cases just too big to put out at the moment," the Bureau of Meteorology said on social media.

"They're pumping out vast amounts of smoke, which is filling the air, turning the sky orange and even appearing like significant rain on our radars."

About 1000 homes have been either damaged or destroyed this bushfire season, while almost 5000 homes have been saved, according to figures released by the RFS on Friday evening.

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