NSW fires, Gospers Mountain fire: Blue Mountains towns under threat | Video

Saturday morning firefighters took advantage of milder conditions and begun conducting backburns along Bells Line of Road with the road closed to all traffic.

However by late Saturday afternoon the fire threat had increased to emergency warning level with the fire spotting across Bells Line of Road.

Residents at Mount Wilson, Mount Irvine, Mount Tomah, Bilpin and Berambing had been told by the NSW Rural Fire Service (RFS) that is was too late to leave.

In a video posted by an RFS member tasked to Mount Tomah on Sunday, a man can be heard saying: "There's spot fires galore down here, we're talking about 60-70 metre flame heights".

Around 11.30pm on Sunday the fire was again upgraded to emergency warning level.

At 7am on Monday the alert was at 'watch and act' with the fire now impacting on Mount Wilson, Mount Irvine, Mount Tomah and Berambing.

"Fire activity has reduced and there is currently no immediate threat," the RFS said.

"Embers may fall in the Bilpin area, and may start new fires ahead of the main fire front."

The fire, which was ignited by a lightning strike on October 26, has so far burnt through 378,695 hectares and stretches from the Lithgow local government area to the Central Coast.

Where conditions allow, firefighters will continue to conduct backburning to protect properties in a number of areas including Bilpin, Itchenstoke, Boree, Bucketty and north-east of Wallerwrang.

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Call triple-0 if you see an unattended fire.