The prime minister, Anthony Albanese, has warned of a “difficult” summer bushfire season ahead, as a natural disaster is declared in parts of New South Wales and crews battling more than 70 fires brace for unfavourable winds on Sunday.

The most destructive blaze – an out-of-control bushfire at Koolewong, not far from built-up areas of the Central Coast – destroyed more than 12 homes on Saturday.

Another four homes were lost at Bulahdelah on the mid-north coast.

Of the active fires, 20 are uncontained. A cool change is forecast to arrive from Sunday morning but forecasters have warned that could create unfavourable conditions, such as strong winds and possible lightning strikes, in places where fires remain out of control.

“We’re not out of the woods yet,” Rural Fire Service deputy co

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