Communities across New South Wales, north of Sydney, have faced relentless downpours since Tuesday, with some areas receiving up to 60 centimetres of rain.
Emergency services have carried out more than 500 rescue operations, including helicopter winches from rooftops.
Taree, Kempsey, and Coffs Harbour are among the hardest-hit towns, with 50,000 residents told to prepare for evacuation or isolation.
Fourteen evacuation centres have opened, and officials warn of further bad news as forecasts predict more rain.