A massive fire front made up of multiple blazes is reportedly closing in on populated areas

It is understood at least eight fires, including a huge 250,000-hectare bushfire at Gospers Mountain, have joined up to create the 60km fire front.

"They are all in a 60 kilometre stretch that runs from the Colo area in the Hawkesbury, north of Sydney, all the way up to near Singleton," RFS Deputy Commissioner Rob Rogers said.

"There is just fire that whole way."

Hawkesbury City Council deputy mayor Mary Lyons-Buckett says the blazes can only be described as a “megafire”.

Firefighters and aircraft working on the Myall Creek Road fire north of Maclean. Hot and dry conditions are fanning the fire. #nswrfs #nswfires pic.twitter.com/UUKx6Nn2Li — NSW RFS (@NSWRFS) December 6, 2019 https://platform.twitter.com/widgets.js

NSW Premier Gladys Berejiklian warned the blaze is closing in to populated areas.

"We have seen the fire is coming to very close proximity to major population centres, whether it is on the South Coast, Central Coast, or even Greater Western Sydney," Ms Berejiklian said.

"We know there have been some property losses, the extent of which won't be known until the fire conditions are safe for people to go in and have a look, but we also appreciate that many families and many people have been asked to leave their homes and we can appreciate what a scary time this is for many people."

The merged fires have now burnt through around 335,000 hectares.