Multiple fires merge together to create fire the size of Sydney

Moment the fire exploded. Photo / Facebook

There are now seven emergency warnings in place as fires burn across the entire NSW coast.

A number of fires raging across the state have merged to create a so-called "megafire", which is burning out of control north of Sydney.

The Gospers Mountain fire burning in the Wollemi National Park, the Little L Complex fire near Singleton and another smaller fire joined together this morning to create a massive blaze.

Rural Fire Service Commissioner Shane Fitzsimons said the blaze now covers more land than all of Sydney, news.com.au reports.

"The Wisemans Ferry area, the back end of the Central Coast, the Colo Heights area on the northern outskirts of Sydney, and the Hawkesbury, all the way through the end of the Central Coast, through the lower Hunter and Upper Hunter area toward Singleton and Muswellbrook," he said.

"We have a significant number of fires which are joining together, and will continue to join together over the coming days and weeks, given the access, the terrain, and the volatility of fire behaviour and how quickly these fires are spreading under hot, dry winds," he said.

"We have fires of concern from the Queensland border to the Victorian border."

Bushfires have now destroyed more than 680 homes in the state alone this season, according to the Rural Fire Service.

A number of fires have merged together. Photo / Supplied

It says almost 250 houses have been damaged, while more than 2,000 outbuildings have been destroyed or damaged.

In the past 24 hours more homes have been destroyed and firefighters have been injured as Australia faces another horror weekend of bushfires.

Seven emergency warnings are in place across NSW, for Howes Valley, Bangala Creek, Kerry Ridge, Carrai East (north west of Kempsey), Boree and Wallabadah, Green Wattle Creek (in the Wollondilly LGA) and the Little L complex in the Yengo National Park area.

Seven more fires are at a "watch and act" level.

NSW Premier Gladys Berejiklian said the fires are currently stretching across the state's entire coastline.

"Currently we have over 90 fires burning throughout the state, about 40 of them are uncontained, but the difference now as we lead into the summer months is, previously there were pretty much confined to the northern part of New South Wales but what we have seen this week is our resources stretched across the entire coastline," she told reporters this morning.

The RFS believes a number of homes have been destroyed in past 24 hours by fires at Shoalhaven's Currowan fire on NSW South Coast and the Three Mile fire in the Hawkesbury.

Elsewhere in the state, three RFS firefighters were injured while battling the blaze at Wattle Creek, near Wollondilly yesterday.

Blazes continue to rage across the nation and the conditions are set worsen, particularly in Queensland.

Firefighters have faced a long night battling blazes stretching from the NSW South Coast all the way to the Queensland border, ahead of yet another day of severe fire danger in parts of the state.

Emergency warnings were at one stage issued for seven bushfires burning in NSW on Thursday, with fires still threatening a number of communities across the state as night fell.

In Queensland, Stifling temperatures are expected to hit this weekend as firefighters continue to battle dozens of fires across the state.

A dire forecast of more severe fire conditions has emergency crews on alert amid concern properties have been lost to a fast-moving bushfire on Queensland's Darling Downs.

Moment the fire exploded. Photo / Facebook

As of Thursday evening, a large fire near Millmerran, west of Toowoomba, had blackened almost 1200 hectares and was raging in the Western Creek State Forest near Cypress Gardens and Forest Ridge.

INCREDIBLE MOMENT FIRE 'EXPLODES'

A photographer has described the intense moment a wall of flames "exploded from the bush" at the Green Wattle Fire on Thursday night, as fire crews fought to battle the blaze.

Sydney Morning Herald photographer Nick Moir tweeted a series of pictures showing a NSW RFS truck holding back flames before an "explosion of fire pushed them back".

It came after a dramatic night as emergency level blazes raged in NSW.

By the early hours of the morning, the Gospers Mountain, Three Mile fire, Currowan fire at Shoalhaven and the Green Wattle Fire and been downgraded to Watch and Act.

Earlier, emergency warnings were issued for a total of seven bushfires on Thursday as hot westerly winds whipped up blaze after blaze.

By 9pm on Thursday night the Currowan fire north of Batemans Bay, the Three Mile blaze and the Gospers Mountain fire close to Sydney, the Green Wattle Creek fire near Warragamba Dam and the Little L Complex Fire near Wollombi were all still classed as emergency warning fires.

"It's going to be a really long night for a lot of communities and the firefighters in those areas," Deputy Commissioner Rob Rogers told the ABC.

"I think the really difficult thing is the amount of fire people have seen since the beginning of August how much fire we've had in the northern part of NSW – well we've just replicated that in the central part of the state as well as still having the north going so it's quite extraordinary conditions."

FEARS OF A MEGA FIRE

The 230,000-hectare Gospers Mountain blaze on Sydney's northwestern outskirts was the first fire to go to the emergency level on Thursday and as the day dragged on there were fears the fire would merge with the 6000-hectare Three Mile blaze near Wisemans Ferry.

Gary Flynn from the Wisemans Inn Hotel said the small town was "dead quiet" as bushfires burned across the Hawkesbury River.

"We are just copping all the smoke," he told AAP on Thursday. "We are just keeping an eye on things at the moment. The town is dead quiet."

On the South Coast between Batemans Bay and Ulladulla, the Currowan fire hit the town of Bawley Point on Thursday with firefighters and residents alike desperately doing what they could to save homes in the coastal town. A number of buildings were destroyed in the area on Thursday, however its unclear at this stage if homes were among the number.

The Currowan fire had destroyed at least one home near the town of Kioloa earlier in the week.

As the fires continue to rage, the longest period of air pollution on record in NSW is set to continue with the Bureau of Meteorology saying heavy smoke from the bushfires ringing Sydney will linger in the city basin until Saturday. Sydney's east and southwest were rated as "hazardous" for air pollution on Thursday while northwestern Sydney was between "very poor" and "hazardous". The lower Hunter and Central Coast also had hazardous air quality. The environment department says this season's bushfire emergency has caused "some of the highest air pollution ever seen in NSW".

"This event … is the longest and the most widespread in our records." Wind gusts of up to 80km/h have been experienced across the ranges with Friday expected to be worse again.

Almost the entire coastal area of NSW and much of the state's northeast have a severe fire danger rating for Friday.

Total fire bans will be in place for the far South Coast and the Monaro alpine, southern ranges, Illawarra-Shoalhaven, central ranges, Greater Sydney, Greater Hunter, northern slopes and northwestern regions.