Backburning destroys 20 homes in ferocious blaze

Up to 20 homes - including those of volunteer firefighters - have been lost north west of Sydney after the Gospers Mountain mega-blaze jumped containment lines and ravaged several Blue Mountains suburbs.

The inferno has also torn through parts of the heritage-listed Blue Mountains Botanic Gardens.

The Rural Fire Service on Monday confirmed that backburning over the weekend spurred the fires, which have damaged around 20 homes.

"Some of our own members appear to have suffered some damage or loss to properties as well," RFS Commissioner Shane Fitzsimmons said.

Blue Mountains Mayor Mark Greenhill on Monday morning said the reports of property loss and "unprecedented" conditions were a sign of "difficult weeks ahead."

An emergency warning was issued by the NSW Rural Fire Service for Mount Wilson, Mount Irvine, Mount Tomah, Berambing and Bilpin on Sunday night with residents told to take shelter.

Ferocious fire columns up to 17m high wreaked havoc on the area as fire crews worked through the night to finally reduce activity to a watch and act level this morning.

The fire this morning crossed the Bells Line of road, placing more homes in the path of destruction.

The Gospers Mountain blaze which is almost 380,000 hectares in size in the Wollemi National Park has been burning since October 26.

On Sunday afternoon it crossed Bowen Creek, south of Mount Wilson and began creating spot fires ahead of the main fire front. One home was seen engulfed in flames while several shed and outlying buildings were lost at Mount Tomah.

NSW Rural Fire Service Commissioner Shane Fitzsimmons said the full extent of the damage is being assessed by specialist teams.

The Blue Mountains Botanic Garden is one of the properties ravaged by the fire, with staff on Monday morning confirming that damage to parts of the garden is "significant."

The gardens are closed due to the fires and staff say they are still assessing the full extent of the damage.

"Thankfully, most of the Garden's Living Collection along with the main buildings are safe at the moment," staff said.

The garden will remain closed for at least another week, according to staff.

The news comes as firefighters prepare for a difficult week with hot and dry conditions sparking severe fire danger across most of the state today.

More than 120 fires are currently burning on the state's east coast and almost half are out of control.

Total fire bans are in place across five districts including the Far North Coast, Central Ranges, New England, Northern Slopes and North Western NSW.

The RFS is urging residents to be vigilant, warning there could be a "flare up" at any time.

At the Gospers Mountain fire, there are fears south-easterly winds later today could push flames into new territory.

More than 1800 firefighters are on the frontline with hundreds more set to join later today.

There is no reprieve in sight for crews with these conditions set to persist through the week with hot, windy and dry conditions on Thursday.

Sydney will swelter through a heatwave later in the week with temperatures set to push into the high 30s in Sydney and suburbs in the west set to nudge 44C.

Northwest and south westerly winds on Thursday afternoon will create difficult conditions for fire crew.

Already 724 homes, 49 facilities and 1582 outbuildings have been destroyed so far this fire season. Six people have died and 2.7 million hectares have been scorched.

The RFS has warned the fire season could be extended by two months, as many of the 104 fires burning across the state will need drenching rain to extinguish.

The bush is so dry it would take 150mm of widespread, drenching rain - equivalent to Two-and-a-half times more rain than Sydney has seen since October - to return to normal moisture levels.