Travellers warned to delay Christmas plans amid catastrophic fire danger

Travellers have been told to delay their Christmas getaway and avoid isolated bush areas as NSW prepares for more "catastrophic" fire danger with authorities saying it'll be a miracle if more homes aren't lost this weekend.

Temperatures are set to soar into the mid-40s and there will be strong winds with the conditions likely to close main highways.

The Greater Sydney, Illawarra-Shoalhaven and southern ranges regions face catastrophic danger on Saturday while the Greater Hunter and central ranges will experience extreme fire danger.

Rural Fire Service deputy commissioner Rob Rogers says homeowners shouldn't expect a fire truck, a plane or a warning to save them "because things move really quickly".

"Do not put yourself in harm's way tomorrow," he said on Friday afternoon.

"Do not put yourself near an isolated bush area. If your home is directly on the bush and it's not got a huge break you should think about relocating."

Authorities are asking people to avoid holiday travel on Saturday because they don't want motorists stranded on major highways when fire fronts hit.

Mr Rogers says it's inevitable that part of the Princes Highway on the South Coast will be closed near Ulladulla.

"We've got problems there with fires to the west that are going to run to the east – we know they're going to impact on the Princes Highway," he said.

There are also concerns the Green Wattle Creek fire, southwest of Sydney, could cross the Hume Highway with Mr Rogers saying there's a "fair chance" it will be closed.

"We will be doing our best to stop it getting across the Hume Highway because if it gets across... that opens up a whole new front for us."

The deputy commissioner said any decision to close major roads would not be taken lightly and the RFS would liaise with NSW Police.

Back burning in the Blue Mountains closed the Great Western Highway in both directions between Blackheath and Little Hartley on Friday evening.

Mr Rogers said the back burn was "simply to try to protect as many properties as we can tomorrow for what we know will be a tough day".

NSW Police deputy commissioner Gary Worboys says motorists may be asked to turn around if they try to enter dangerous areas.

"People should consider staying at home tomorrow and make their travel arrangements for Sunday, Monday and Tuesday," he said.

"They still have time in terms of Christmas Day. Tomorrow will be a difficult day."

Residents should instead go to the beach, a shopping centre or somewhere else safe.

‘Fairly sure thing we’ll lose homes tomorrow’

Almost 800 homes have been lost in NSW so far this bushfire season and that number is almost certain to rise on Saturday.

"It's a fairly sure thing we will lose homes somewhere tomorrow," Mr Rogers said

"It would be a miracle if we didn't."

A week-long state of emergency has been declared and a statewide total fire ban remains in place.

The catastrophic rating comes after two firefighters were killed in the battle to contain the Green Wattle Creek blaze that ripped through villages southwest of Sydney on Thursday.

Geoffrey Keaton, 32, and Andrew O'Dwyer, 36, from the Horsley Park brigade were in a truck convoy near the town of Buxton when a tree fell, causing their vehicle to roll off the road.

All national parks in Greater Sydney are closed from Saturday until further notice, the state's environment department announced on Friday.

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