A woman in her 30s has died after being struck by a falling tree branch in the Watagans National Park.

The woman was bushwalking at Cooranbong near Lake Macquarie around 6:30pm on Sunday night when the branch fell.

Police, paramedics and officers from Fire and Rescue NSW responded to the report but despite the efforts of relatives and first responders she could not be revived.

Adverse conditions drenching the area with heavy rain may have contributed to the tragedy, and a report will be prepared for the Coroner.

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