Taree, about 300km north of Sydney, is a key area of concern for emergency services after 415mm of rain lashed the town since Monday – more than four times the mean monthly rainfall for May.
Authorities said water levels of a river in Taree surged past a previous record in 1929, reaching 6.3m on Wednesday.
The rising floodwaters left locals stuck on roofs overnight, with rescuers unable to reach them because of the bad weather.
Taree resident Holly Pillotto, who was among those stranded on an upper level of her home, said she was desperate for assistance as floodwaters continued to rise.
“Our neighbours on the back verandah here are also stranded,” she told Australia’s Channel Nine. “It’s a really dangerous spot to be.”
Dib said emergency services were “throwing everything we have” into reaching those affected.
State Emergency Services chief superintendent Dallas Byrnes said the situation was “incredibly dynamic and escalating”, with more than 150 flood rescues conducted overnight.
“We’ve got a lot of people getting rescued from rooftops and from upper levels of houses,” Byrnes told the national broadcaster ABC.
However, he warned that “conditions are quite treacherous and it may be that those aviation assets are unable to fly throughout the day”.
The agency said about 16,000 people, or 7400 dwellings, would remain isolated until at least Thursday.
More heavy rain is expected in the coming 48 hours, with some locations to receive 200mm before conditions begin to ease, authorities said Wednesday.
Scientists have warned that heatwaves and other extreme weather events are becoming more frequent and more intense as global temperatures rise because of climate change.
– Agence France-Presse