More than 100,000 homes in the Sydney basin alone are within 100 metres of bushland, placing them at risk of destruction based on previous bushfire activity.

Data from the consultancy Risk Frontiers identified premises exposed to extensive bush. Of the total, more than 31,500 homes on Sydney's north shore were in "at-risk" areas - from Belrose to Berowra, and south to Lane Cove - while Turramurra had the most homes nestled near bush with some 4500 residences.

A common sight after the October 2013 bushfire swept through parts of Winmalee in the Blue Mountains. Credit:Dallas Kilponen

"Analysis by Risk Frontiers of major historical bushfires shows distance from the bushland fringe to be the single most important factor determining the probability of building destruction given an extreme fire in adjacent bushlands," the group's general manager Andrew Gissing said.

"The vast majority of homes that are destroyed in fires are within 500 metres of bushland," he said, noting that in the 2018 Tathra bushfire some 73 per cent of properties destroyed were within 100 metres and no home was razed further than 630 metres.