Early season heat, rapidly drying forests on Sydney's rural edge and a shortfall in hazard-reduction burning during the autumn and winter are combining to raise the threat of big bushfires.

As of Friday afternoon, 45 fires were burning across the state, 14 of them uncontained, the NSW Rural Fire Service said. Crews were also preparing for an uptick in bushfire danger over the weekend particularly in the north where blazes have charred more than 130,000 hectares, some of it ancient Gondwana rainforest.

Firefighters battle bushfires in Angourie, northern NSW. Credit:AAP

Katoomba in the Blue Mountains and the north-west region near Richmond are notably dry.

Ross Bradstock, director of the Centre for Environmental Risk Management of Bushfires at the University of Wollongong, said "it’s a matter of weeks now" before the recent severe fire weather made its way south to Sydney.