Firefighters are warning NSW residents to brace themselves for heatwave conditions that are forecast to fan more than 100 bushfires raging across the state.
The NSW Rural Fire Service on Tuesday issued a four day state-wide total fire ban from Wednesday to Saturday due to hot and dry conditions.
"There are difficult and dangerous fire conditions forecast over coming days," the RFS tweeted.
Some 109 fires are currently burning across the state with 64 uncontained.
The huge Gospers Mountain blaze northwest of Sydney and the Forest Road Fire at Comberton were both at "watch and act" alert levels at 7pm on Tuesday evening.
More than 2300 firefighters are in the field, desperately trying to contain the fires before the worst of a heatwave spreading across the nation hits on Thursday.
"Reality is we are doing our best to get as far ahead as we can but they're not going to be contained before the bad weather hits," an RFS spokeswoman told AAP.
Daytime temperatures in NSW and the ACT are expected to exceed 40C from Tuesday through to Saturday while in the western half of the state the mercury is set to top 45C.
The heatwave will likely spark an elevated fire risk across NSW, the Bureau of Meteorology and NSW Health have warned.
"With the heat comes fires so we're expecting some particularly tricky days for the fire response on Thursday, Friday, Saturday and Sunday," BOM acting NSW manager Jane Golding told reporters.
NSW Rural Fire Service deputy commissioner Rob Rogers says firefighters will not be able to contain every blaze before conditions deteriorate.
"While we're very concerned about the Gospers Mountain fire, there are more than 100 fires burning throughout the state," he told reporters.
"Anyone of them could cause problems over ensuing days."
The Gospers Mountain blaze destroyed up to 20 buildings in the upper Blue Mountains on the weekend after firefighters lost control of a backburning operation and the fire jumped containment lines.
It is burning on multiple fronts from the Lithgow area in the west, through the Hawkesbury area and towards the Central Coast in the east. It's so far destroyed more than 400,000 hectares.
Nearby, the Mt Piper Power Station continued to operate on Tuesday afternoon with only essential personnel, an EnergyAustralia spokesman said in a statement to AAP.
"Our priority is keeping our people safe and we are liaising with the NSW Rural Fire Service," he said.
NSW Health's environmental health director Richard Broome said smoke was expected later in the week as temperatures soared.
He said smoke pollution had created an "unprecedented emergency", adding "we haven't seen conditions like this in Sydney, certainly anyone's memory that I've spoken to".
Premier Gladys Berejiklian says NSW is resourced to meet the crisis.
Six people have died in bushfires so far this season and more than 720 homes have been lost.
Meanwhile, eight adult and four joey koalas from the Blue Mountains Kanangra-Boyd National Park, considered critical to the survival of the koala species due to their genetic diversity and the fact they're one of only two Australian koala populations that are chlamydia free, have been rescued by a conservation group.
The koalas' home is currently being threatened by the Green Wattle Creek fire which has already burnt through 140,000 hectares of parkland.