Three major bushfires burning north of Sydney have united to create what has been called a “mega blaze” that has so far burnt more than 300,000 hectares of land.

The new mega blaze was formed when the Gospers Mountain fire in the Hawkesbury region merged with the Little L Complex blaze and the Paddock Run fire near Singleton, both in the Hunter.

The single fire front, which covers an area bigger than greater Sydney, was at emergency level on Friday afternoon and threatens major population centres.

AT 4pm ADST Friday, there were eight other emergency warnings for fires in NSW, with conditions expected to deteriorate on Friday afternoon.

At 4pm there are nine fires at Emergency Warning and nine at Watch and Act. Of a total of 108 fires, 74 are not contained. More than 2,800 firefighters are facing challenging conditions with hot temperatures & strong winds. There is a lot of smoke around Sydney. #nswrfs #nswfires pic.twitter.com/Uf1USjPERX

— NSW RFS (@NSWRFS) December 6, 2019

ABC weatherman Graham Creed pointed out that if “85 per cent of NSW population lives within 50 kilometres of the coast, that means 6.8 million people are under some level of threat of direct impact or health issues related to bushfires”.

On Thursday, the NSW Rural Fire Service issued emergency warnings for seven fires, including two threatening areas on Sydney’s doorstep.

RFS commissioner Shane Fitzsimmons said Friday would be “another extremely busy day” with temperatures reaching into the high 30s in some places coupled with very low humidity.

“We can’t overstate the effect that this profound drought is having … on the flammability of the fuel,” he said.

“You are seeing fires start very easily and they are spreading extremely quickly and they are burning ridiculously intensely.”

Starting to see increasing #bushfire activity across the state. Now have another fire in #NSW just climbed back to #Emergency #Warning level. The situation continues to remain volatile. For the latest updates keep an eye on @NSWRFS at https://t.co/xVB1NwiNST

— Bureau of Meteorology, New South Wales (@BOM_NSW) December 6, 2019

Emergency warnings were also current on Friday for the Kerry Ridge fire in the Wollemi National Park, the Carrai East blaze northwest of Kempsey and the Bangala Creek bushfire near Tenterfield.

There are also a further seven major fires at “watch and act” level.

NSW Premier Gladys Berejiklian said many families had been forced to leave their homes and take refuge in emergency shelters or with friends and family.

“Our thoughts are with the people who have been displaced and people who are living in fear … and we have to acknowledge many people throughout the state are,” she said.

This video shows the dangers of embers being blown ahead of some of the large fires burning across NSW. This is the Green Wattle bush fire burning near Lake Burragorang. The fire is impacting on the area around Nattai.#nswrfs #nswfires pic.twitter.com/92n2ymWbS5

— NSW RFS (@NSWRFS) December 6, 2019

There were more than 90 fires burning across NSW on Friday, 40 of them uncontained.

“Previously they (bushfires) were pretty much confined to the northern part of NSW but what we are seeing this week is our resources stretched across the entire coastline,” Ms Berejiklian said.

“We’ve also seen the fire come into very close proximity to major population centres.”

The NSW Rural Fire Service said on Friday that more than 680 homes had already been destroyed by bushfires this season, and six people had died.

Almost 250 houses had been damaged, and more than 2000 outbuildings destroyed or damaged.

More properties are thought to have been lost or damaged on Thursday, particularly at Bawley Point north of Batemans Bay, but exact figures will not be known until assessment teams can safely enter the burned-out areas.

Firefighting crews have come from interstate as well as New Zealand and Canada to help fight the NSW bushfires and were being briefed on Friday morning. A team from the US will arrive on Saturday as the fire threat continues over the weekend.

Ms Berejiklian has repeatedly said now is not the time to talk about the impact of climate change on bushfires.

But according to a UNSW community survey released on Friday, 53 per cent of respondents say it is right to talk about global warming during extreme events.

Just 35 per cent of Australians surveyed said it’s not OK.

Almost the entire coastal area of NSW and much of the state’s north-east is under a severe fire danger rating, while total fire bans are in place for the southern ranges, Illawarra-Shoalhaven, Central Ranges, Greater Sydney, Greater Hunter, Northern Slopes and northwestern regions.

-with AAP