Heavy rainfall, flash flooding and river flooding reaching moderate to major levels is forecast for parts of the Hunter, Mid North Coast and Northern Rivers today.
The Bureau of Meteorology has several weather warnings in place across the state, including for damaging winds.
Gusts of more than 90 km/h are possible for coastal areas between Gosford and Coffs Harbour.
A Hazardous Surf Warning is also in place, with dangerous conditions expected for swimmers, fishers and boaters in the Hunter and on the Mid North Coast.
Marine Area Command says people should avoid swimming and walking near surf-exposed areas.
For more information, visit the Bureau of Meteorology website.