Part of the New South Wales north coast was declared a natural disaster zone on Wednesday after flooding described as once-in-a-century.
The weather bureau issued a severe weather warning on Wednesday for flash flooding, damaging surf and gale-force winds from Sydney to the mid-north coast.
The Bellinger River peaked at 8.6 metres, stranding more than 3000 people, after 400 millimetres of rain fell in 24 hours.
More than 2200 people are expected to remain stranded for two to four days.
Authorities have closed all Sydney's beaches, except for Bondi, because of waves up to 5 metres high.