Floodwaters at Tamworth in New South Wales were receding on Sunday, a day after a natural disaster zone was declared.
The flooding trapped people in their homes and cars and cut off part of the town.
The Peel River peaked at 5.9 metres about 9am (AEDT) on Saturday after more than 200mm of rain deluged the area in 36 hours, causing widespread flash flooding.
Emergency Services Minister Tony Kelly declared the area a natural disaster zone, promising financial assistance for residents and business owners devastated by the flooding.
A state emergency service spokeswoman, Erin Pobmore, said the main concern on Sunday was now the nearby area of Gunnedah.
Ms Pogmore told the ABC the floods would spread to other parts of the region on Sunday, and road closures were expected.
Mr Kelly earlier said available assistance to the Tamworth region could be extended, depending what happens in Gunnedah.
An emergency services spokeswoman said the service had taken almost 170 calls for help on Saturday, mainly to help patch up leaking roofs and assist with sandbagging.
"People stranded across causeways, people who have been washed off causeways, people in trees, people trapped in vehicles," a local SES controller told ABC Radio on Saturday.
Eleven people have been rescued from floodwaters, including a grandmother and her 10-year-old grandson who were washed from their vehicle on a flooded causeway, Mr Kelly said.
He said the floodwaters had caused extensive road damage, with many roads washed out.
All access routes except the main bridge into Tamworth had been cut and the Oxley Highway was closed for some time but had since reopened.