Properties in rural NSW have been evacuated and families in others are preparing to move out as much of the state is ravaged by flood and severe weather.
A vast, slow-moving cloud band across much of southern and western NSW has caused heavy rainfall and flash flooding, with 70 people evacuated to Cowra Library overnight on Wednesday.
Evacuation warnings are also current for Goulburn and Cooma where around 100 properties are affected and a major flood watch is in place.
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Downstream from Jerrara Dam people are being told to prepare for evacuation, with 10 properties affected.
"Volunteers have been deployed across the state, covering some of those hot spots," NSW State Emergency Services (SES) Andrew
Richards told AAP on Thursday.
"They are out this morning knocking on doors trying to prepare residents."
Warragamba Dam, which is currently at 89.2 per cent capacity, is expected to spill for the first time since August 1998.
Floodgates are scheduled to be tested for two hours from 8am (AEDT), with staff anticipating dam levels at one metre below full storage.
Kerrie Karma Nichols said her parents at Wallacia in Sydney's west, on the Nepean River, were expecting their house to be inundated once the dam spills.
"They go under first when the Nepean breaches it banks," Ms Nichols said on Facebook.
"We are expecting their house to go under as soon as the Warragamba Dam breaches capacity sometime probably in the next 24 hours."
Overnight falls were not as bad as expected but are set to continue into next week, with flood warnings on many of the state's river systems.
A severe weather warning remains in place for much of NSW, including the Illawarra, Snowy Mountains and South coast.
"Four day totals from Wednesday through to Saturday are expected to be in the range of 100 to 30 mm within the warning area, with isolated larger totals possible," the Bureau of Meteorology (BoM) said.
"The Illawarra, Southern Tablelands, Snowy Mountains, South Coast and southern Central Tablelands districts are likely to have some locations receive in excess of 100mm on Thursday."
Sheep graziers are being warned of a cold snap, heavy rain and southerly winds during Thursday on the south coast, the southern tablelands and in the Snowy Mountains, with parts of the Riverina, Illawarra and South West Slopes also affected.
"There is a high risk of losses of lambs and sheep exposed to these conditions," the BoM said.
As rain continues to lash the state, the SES has been inundated with more than 700 calls for assistance since Monday afternoon.
Since the beginning of the week, two people have been rescued from a house in Koorawatha, south of Cowra while two adults and two children were rescued from the roof of a vehicle in Koorawatha after they were stranded in floodwater.
Another five people were also rescued from a roof in Koorawatha and four more were helped when their vehicles were stranded on a flooded road in Young.
