Blue Mountains towns are bracing for a heightened fire threat as bushfires expand and communities count the cost after yet more homes were lost.

The communities of Bilpin and Berambing were mostly populated by fire crews and police on Monday, after a backburn aimed at containing the giant Gospers Mountain fire crossed containment lines, destroying homes and scorching part of the Blue Mountains Botanic Garden at Mount Tomah.

Kurrajong Heights firefighters work on burnt-out bushland at Berambing on Monday ahead of ominous forecasts this week. Credit:Dean Sewell

The Herald saw several homes along the nearby Skyline Road completely razed before police closed access to the previously-scenic pass.

"We're all exhausted," said Brian Williams, a local RFS firefighter and vice president of the Volunteer Fire Fighters Association. "It's becoming a drain."