"Worst ever" and "unprecedented" have become the new norm this bushfire season, but when a blaze grows to the size of Sydney a new standard of overwhelming is set and firefighting becomes a logistical headache.

Five blazes merged north of Sydney on Friday and the term "mega-fire" reared its ugly head.

The 60-kilometre fire front continues to consume areas west of Gosford, including Colo Heights, Wollangambe, Mellong, Wollemi and Big Yengo.

But how exactly does the Rural Fire Service (RFS) fight a fire this big?

Uncharted territory

This 250,000 hectare blaze has presented new challenges for the RFS and different approaches must be taken, according to public liaison officer Stuart O'Keefe.

A Rural Fire Service volunteer uses a drip torch during back-burning operations in 2013. ( ABC News: John Donegan )

"This is all relatively new, but based on smaller files we just need to expand our thinking to a degree," he said.

The RFS maintains they are up to the challenge and extensive consultation, smart rostering and forward planning are paramount.

But put simply, there is no chance firefighting resources can match the scale of this fire, and to do so every firefighter in the state would have to be deployed to the area.

And with nearly 100 fires burning across the state that is an impossible ask.

The tactics

The sheer magnitude of this fire does not dramatically alter the type of firefighting techniques used.

"It's no different if it's one hectare or 260,000 hectares when it comes to strategies," Mr O'Keefe said.

Water is still king, but it's a drop in the ocean on this scale.

Crews can only get 30 to 60 metres away from a truck, so the impact is minimal.

"Then you need another truck, and another, and another. And with so many fires, the demand for trucks can't be met," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 11 seconds 1 m 11 s Fire retardant dropped on fires and residential houses in Sydney last month. ( ABC News )

So building containment lines with bulldozers can be more reliable.

But this means heavy machinery has to be sourced from the local communities, which takes up precious time as nothing is "just around the corner" in this rugged, remote area.

Aerial firefighting bought some time, but Mr O'Keefe emphasised that retardant did not extinguish a fire — just slowed it.

The ultimate question: how long?

Saturday's easing conditions have provided some firefighting relief and allowed for a concentrated effort on backburning.

But it's a see-saw, with conditions set to worsen again next Tuesday.

"Peoples' emotions are very, very tested and frail at the moment," he said.

Basically, it could get better just to get worse, and it is anyone's guess when this fire stops growing.

That's bad news for those on the Central Coast and in Sydney who are being choked by smoke from these blazes.

There was realistically only one remedy, Mr O'Keefe said, and it had nothing to do with tactics.

"We need flooding rain to put these fires out. That's really what is going to stop it."