NSW firefighters battling more than 100 blazes which could take 'many weeks' to quash

Firefighters say rain is the best hope of putting out the massive Gospers Mountain "mega-fire" near the outskirts of Sydney.

Long exposure photograph shows the Three Sisters rock formation as flames from the Kowmung River fire and the Green Wattle Creek fire are seen from Echo Point. Source: AAP

More than 100 fires are burning across NSW including a "mega-fire" the size of Sydney as authorities brace for temperatures to soar into the 40s early next week.

The Gospers Mountain "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 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 on Friday evening.

NSW Rural Fire Service crews fight a fire as it burns close to property on Wheelbarrow Ridge Road at Colo Heights. Source: AAP

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

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

At one point on Friday, nine fires were burning at an emergency level and more than 100 fires burning across the state.

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

Total fire bans are in place on Saturday for the far north coast, New England, the northern slopes, the greater Hunter, greater Sydney, the central ranges and the northwestern regions.

Meantime, a pilot has walked away and escaped serious injury after a NSW Rural Fire Service helicopter crashed north of Newcastle on Saturday.

The man, who was the only person on board, was taken to John Hunter Hospital in Newcastle as a precaution after a hard landing at Crawford River on Saturday.

The helicopter, believed to be a waterbomber, was helping to battle a fire at Jarrah Road, Girvan.