UP TO 80 blazes have destroyed upwards of 40 homes throughout NSW in what the Rural Fire Service said was the most serious fire threat to the state in a decade.

More than 600 firefighters were thrown into battle and thousands were evacuated from their homes as major blazes burned at the Blue Mountains, near Newcastle and in the Southern Highlands.

"If we get through with less than 100 homes destroyed today, we have been lucky," Rural Fire Service Commissioner Shane Fitzsimmons tweeted.

Ash and bloom fell from the sky as far east as Sydney with the city's famous Harbour an unusual shade of brown.

Here's what you need to know:

media_camera A large bushfire near the Williamtown Airport near Newcastle. Picture: John Grainger

media_camera Covered in smoke ... The scene in Sydney this evening. Picture: Damian Shaw

1. There are seven major blazes across the state as of 5:30pm (AEST): Mt York Rd in Mt Victoria, Quinn's Lane in South Nowra, Hall Road in Balmoral Village, Andrews Road in Varroville, State Mine in Lithgow, Linksview Road in Springwood, and Hank St in Heatherbrae

NSW Rural Fire Service Deputy Commissioner Rob Rogers said: "It's probably the most serious fire risk we've faced since the early 2000s."

Fire tankers are being diverted to head towards new houses under threat in Emma Parade , Winmalee, where the RFS FireComms line reported houses are burning.

2. Lives in danger: There are have been no reports of loss of life.

The RFS has sent an emergency warning to Blue Mountains residents warning them to postpone non-essential travel.

RFS radio reported "persons frantically requesting our assistance" trapped inside a brick and tile home which was "well alight".

A firefighter is being treated for smoke inhalation at Winmalee in the Blue Mountains.

3. Multiple homes lost: Upwards of 40 homes were engulfed in flames in Springwood alone.

Houses were engulfed in the lower Blue Mountains suburb of Winmalee and Springvale, with homeowners evacuated to nearby public schools and shopping centres.

The fire is now threatening suburbs around Penrith after flames leapt across the Nepean River and put homes at Castlereagh and Emu Plains at risk.

There are also unconfirmed reports of homes being destroyed at Lithgow and Mt Victoria, with fire crews battling an out-of-control blazes on two fronts. The Lithgow fire is still out of control and headed towards Mt Tomah.

Properties have also been reportedly lost at Yanderra and Balmoral in the Southern Highlands.

3. We need rain. "Nothing short of torrential rain will ease things at the moment," RFS Deputy Commissioner Rob Rogers told ABC Local Radio.

A southerly was scheduled to hit around 5pm AEST.

Rural Fire Service spokesman Anthony Clark told AAP it was a critical time.

"The key thing is with that change coming through, (these are) really dangerous conditions for the next couple of hours," he said.

4. The NSW Rural Fire Service website has crashed. Go to google.org/crisismap, the RFS Facebook page or follow its Twitter feed for updates.

media_camera The blaze seen from an oval in Springwood. Picture: Twitter

@newscomauHQ Penrith - you'd swear there was a fire right near my house! The great western highway is parallel pic.twitter.com/tIm2huFO2T — Rachel Moor (@rachjmoor) October 17, 2013

Loud explosions frequently heard looking toward Yellowrock from Warrimoo Oval #nswfires #nswrfs pic.twitter.com/WMj80BY8C3 — dann weatherhead (@weatherhead) October 17, 2013

Photo doesn't do it justice but re sun is bright red pic.twitter.com/8gJ2CnpvxW — Rob Stott (@Rob_Stott) October 17, 2013

Joe Moore, a golf professional from Springwood Country Club, told Sky News of his terrifying ordeal as his house burned down this afternoon.

Mr Moore has lived his whole life in Springwood - a town in the lower Blue Mountains - and spoke in emotional tones from Springwood Country Club, which is a safe haven for members of the community who have been evacuated.

"I was on the phone to my son about 15 minutes ago and the firey said to my son Kevin 'We can't save your house Kevin, get out no'.

Mr Moore said he had been watching the fires in Lithgow about 50 km to the west, on the far side of the Blue Mountains.

At that point he did not realise his own neighbourhood was under threat.

"We were watching the Lithgow fires jumping up over the mountains, when all of a sudden 100km winds soon got out of hand and before you knew it we were on fire again.

"It was nearly the perfect storm, high winds, dry leaves on the ground and massive winds and fires out of control.

"I've been told there are nearly 40 homes lost already."

Loud explosions frequently heard looking toward Yellowrock from Warrimoo Oval #nswfires #nswrfs pic.twitter.com/WMj80BY8C3 — dann weatherhead (@weatherhead) October 17, 2013

@newscomauhq @702sydney Pic of pyrocumulus cloud generated by Shoalhaven fire from flight home from Melb. pic.twitter.com/AIGI5jyHaF — Dan (@Dan_Meijer) October 17, 2013

media_camera The weather radar picked up the ash on its radar. Picture: Supplied

media_camera Fire threatens Williamtown airport. Picture: Craig Meyers/Twitter

EARLIER UPDATES (3pm AEST):

Across the state 595 firefighters battled at least 78 bush and grassfires, 31 of them uncontained.

Strong, hot and dry winds hampered firefighting efforts.

NSW Premier Barry O'Farrell has encouraged MPs whose electorates are affected by bushfires to leave parliament and help where they can.

In parliament, Mr O'Farrell encouraged MPs whose electorates were affected to leave.

"There is not much we can do except wish those extraordinary volunteers and paid firefighters out there every success and every luck," he said.

"There have been suggestions already that some of these fires may well be the result of arson.

"Hopefully that is not true; hopefully it is down to today's weather conditions."

media_camera Bushfires Southern Highlands. Traffic is halted 2kms outside of Bargo turnoff as a bushfire runs through Balmoral Village and Yanderra.

The premier said a southerly change was not expected in Sydney until 5pm.

"Until that stage, this city can't rest easy," he said.

"There are parts of the state where currently residents are battling the uncertainty of the outbreak of these fires and our hearts and our thoughts are with them."

About 8700 homes west, south west and north of Sydney are without power, with wind gusts of up to 70km/h bringing branches down on powerlines.

Endeavour Energy on Thursday advised members of the public to stay well clear of fallen powerlines.

It has also advised residents in Lithgow, where a bushfire is burning, that it might need to isolate parts of its network as the fire passes through.

In the Blue Mountains, power has been cut to about 4500 homes and businesses in Katoomba, Winmalee and parts of Leura, Blackheath and Mt Victoria.

media_camera Traffic is halted 2km outside of Bargo turnoff as a bushfire runs through Balmoral Village and Yanderra in the Southern Highlands.

In the Macarthur region, crews are working to restore power to about 1600 homes and businesses.

The worst affected areas at this stage are Wilton, Menangle and parts of Campbelltown.

In the Hawkesbury, strong wind has interrupted electricity supply to 1300 homes along the Hawkesbury River from Lower Portland and Maroota to St Albans.

Fallen powerlines can be reported by calling 131 003.

In the Southern Highlands, south-west of Sydney, a fire at the village of Balmoral, in Wingecarribee, was moving very quickly.

media_camera Emergency warnings for Newcastle, Blue Mountains

Rural Fire Service spokesman Joel Kursawe says there are reports one house is on fire.

"They're saying that one house is already alight, that could be because the house was alight and it's spread, or not, we don't know," he told reporters.

"It's all happened very quickly."

Attempts to waterbomb in Lithgow were being hindered by 90km winds, Mr Kursawe said, which were also capable of carrying embers up to six kilometres.

media_camera Smoke from rhe Balmoral Village and Yanderra bushfire blankets the horizon.

"The problem is when you've got aircraft over fires like that with (those) winds, a lot of the time they're just getting knocked around in the sky," Mr Kursawe told journalists at RFS headquarters in Sydney.

RURAL FIRE SERVICE MAP OF CURRENT FIRES AND INCIDENTS

Homes at Clarence, Dargan, Doctors Gap and Hartley are expected to come under threat from the fire, which has already burnt more than 1000 hectares of bushland.

Two evacuation centres have been set up at Lithgow Workers Club and Mt Tomah Botanic Gardens.

Meanwhile, more than 130 firefighters are fighting the blaze near Port Stephens.

"Some of the pictures we're getting from up there, it's just incredible," Mr Kursawe said.

"It's just a mass smoke cloud over the whole town."

The fire at Balmoral Village was approaching the township of Yanderra and residents were being urged to move towards Bargo.

A total fire ban remains in place for several areas of the state with temperatures of 34C forecast.

It was nudging 34C in Sydney at 1pm (AEDT) with gusty winds.

media_camera The Heatherbrae bushfire near Williamtown Airport in Newcastle. Picture: Twitter

Of most concern to firefighters are three fires.

In the Blue Mountains west of Sydney, near Lithgow, more than 100 firefighters are battling a massive blaze that is skirting the village of Oaky Park and spotting into Clarence.

A new fire had also broken out at Springwood.

RFS deputy commissioner Rob Rogers tweeted: "lithgow fire becoming unpredictable. Residents please take extreme care. Very serious danger to life today".

A Blue Mountains resident said the RFS had just knocked on his door warning the fire was approaching.

"The sky is very dark with the sun burning orange through the dark smoke," the resident told ABC radio.

Bells Line of Road has been closed between Lithgow and Bell in both directions.

The Darling Causeway is closed northbound at the Great Western Highway in Mount Victoria.

NSW National Parks and Wildlife Service has closed additional areas of the Blue Mountains National Park because of the threat.

#Lithgow Fire: People in the area around Doctors Gap should be alert to smoke and burning embers. Seek shelter as the fire impacts #nswfires — NSW RFS (@NSWRFS) October 17, 2013

Blue Mountains Regional Manager Geoff Luscombe said all tracks and trails in the Grose Valley, as well as lookouts along the Bells Line of Road, are now closed as a precautionary measure.

"With a very high fire danger rating there's always a chance that the Lithgow fire could enter the park and if that happens we don't want people walking in there,'' he said.

Residents who hadn't already evacuated before noon were advised to take shelter in their homes.

And at Port Stephens, north of Newcastle, Williamtown Airport was closed about midday and all flights in and out were suspended because of a bushfire burning nearby.

Passengers are advised to not come to the airport and to contact their airline for flight details.

Smoke from the Port Stephens fires, not far from where four homes were lost on Sunday, was visible from the Newcastle CBD.

media_camera The dramatic scene at Williamtown Airport, Newcastle. Picture: Twitter @WynRichards

Similar conditions on Sunday resulted in six homes being lost to fires at Port Stephens, north of Newcastle, and near Kempsey on the north coast.

The airport was closed after a fire burning near Heatherbrae breached containment lines fanned by gusty winds, the RFS said.

Properties around Tomago Road, Cabbage Tree Road, Barrie Close, and Williamtown Drive may also come under threat, the RFS warns.

Smoke from the fire is visible from the Newcastle CBD.

In the Blue Mountains region, residents of Clarence and Oaky Park have been urged to seek shelter and protect themselves from flying embers, with properties there expected to be threatened.

Emergency Warning - State Mine Fire (#Lithgow) http://t.co/aMz0YfuiCi The fire has now crossed the Bells Line of Road and is out of control. — NSW RFS (@NSWRFS) October 17, 2013

Those who had planned to leave their homes in a bushfire should have left by noon (AEDT), NSW Fire Commissioner Shane Fitzsimmons said.

Conditions were worsening with winds expected to reach up to 95km/h.

"History will show, too many lives are lost when people flee at the last minute,'' he said.

The fire broke out near an army range on Wednesday afternoon, with explosions and detonations making it too dangerous to send in firefighters and aircraft.

Mr Fitzsimmons says the fire would take some time to control given the sweltering conditions and its geographic location.

It's expected to skirt to the northeast of Lithgow and head into the mountains as the winds pick up.

Conditions were worsening this afternoon with winds expected to reach up to 95km/h.

If the high winds do fan the blaze, it could disrupt the Western rail line through the area, Mr Fitzsimmons said.

A 367-hectare bushfire is also burning 15km east of Singleton, in the Hunter Valley, but is being controlled.

Originally published as Major bushfires burn out of control