Communities along the Hawkesbury River in NSW are bracing for once-in-a-generation flooding that could displace residents and disrupt utilities for months.
The Bureau of Meteorology expects Monday to bring the worst flooding event to the area northwest of Sydney since November 1961, nearly 50 years ago.
Floodwaters are expected to rise to major levels on Monday morning and inundate places such as Windsor, Pitt Town, North Richmond, Freemans Reach and Colo.
The Hawkesbury is predicted to reach peaks of up to 15 metres and the State Emergency Service says homes and properties will be flooded, some up to roof height.
The floods will cut off evacuation routes and cause lasting outages to utilities, the SES said as it urged residents to prepare to evacuate.
"Extensive outages of water, electricity, sewerage, telecommunications and gas are expected to last many weeks or months," the SES said early on Monday.
The event is likely to exceed the capacity of emergency crews, who have already responded to some 8000 calls for help, the SES said.
Flooding along the Hawkesbury and Nepean rivers comes after the Warragamba Dam spilled over, prompting some concern.
Parts of Penrith and other areas along the Nepean were ordered to evacuate on Sunday as NSW battles devastating floods after days of unabated rain.
Scores of people have already been rescued from floodwaters, while prison inmates have been evacuated and more than 100 schools remain shut.
Those saved include an 80-year-old woman who became trapped in her car at Wyong on the Central Coast on Sunday.
Police spotted the half-submerged car while attending to another incident nearby and realised the driver was still inside.
An officer waded out into the waters on foot and freed the woman before the car was pushed by the fast-moving waters into the nearby Wyong River.
BOM's Agata Imielska said the severity of rainfall in greater Sydney would ease on Monday but the mid-north coast would continue to be drenched and inland NSW would be pounded by rain.
She said the NSW northwest slopes and plains would receive four times more rain in two days than the entire March monthly average.
Premier Gladys Berejiklian earlier said the floods in the Hawkesbury Nepean Valley could prompt an additional 4000 evacuations.
Parts of Port Macquarie, Taree and nearby towns have also flooded in what Ms Berejiklian labelled a "one-in-100-year event" for the region.
The federal government's natural disaster arrangements have been activated for 18 local government areas across NSW.
Australian Associated Press
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