Residents of Picton in south west Sydney have been told to evacuate before it becomes "too dangerous" as rising flood waters threaten to inundate the area.
"Residents should monitor the situation and be prepared to evacuate when instructed to do so," the SES said on Sunday morning. "A Flood Evacuation Order will be issued by the NSW SES if evacuation is required.
"Once floodwaters begin to rise in Stonequarry Creek you will see flooding of roads, sewerage lines and power may be lost, and properties to be inundated. If you remain in the area you may become trapped and it may be too dangerous for NSW SES to rescue you."
Homes are also being inundated at Raymond Terrace and Hinton in the Hunter region, and concerning major river rises are also occurring at the Hawkesbury River and Wauchope.
Queensland's Premier Annastacia Palaszczuk said SES boats and crews will be sent to NSW to assist with multiple emergency flooding events as heavy rainfall is forecast to continue into next week.
The Bureau of Meteorology says weather situation is "volatile, dangerous and dynamic" as another wave of powerful rain approaches.
"Numerous warnings are in place & we're urging people to keep watch as the situation continues to evolve through tonight," a spokesperson said in a tweet.
Some incredible footage has emerged from the flooding, including a home lifted off its foundations yesterday and being carried down the Manning River in the Mid-North Coast district of New South Wales.
The couple who were renting the house at Mondrook, near Taree were due to be married there yesterday. Sarah Soars and Joshua Edge were not home at the time, but their pets and all their possessions have been lost.
An online fundraising page for the couple has surpassed its A$30,000 target.
The couple's landlords Peter Bowie and Tracia Milton, who are new to the area, told ABC News they have lost 180 cattle in the floodwaters.
Tracia said watching the house get swept away was 'devastating'.
The NSW State Emergency Service has been inundated with calls for help in recent days as wild and unpredictable weather lashed the state.
The SES received some 750 calls for help on Saturday night, talking the number of calls since Thursday to more than 4500, Daniel Austin, NSW SES Deputy Commissioner told the ABC. He said the calls were showing "no sign of letting up any time any time soon".
He said the 1500 volunteer responders were dealing with "some pretty phenomenal conditions" in "some very, very trying circumstances".
"So in amongst all this, we still attended road crash – road accidents and the like throughout the state, but we're also then still dealing with trees down, power outages in places and helping the electricity companies through clearing of debris there.
"Damage to houses. We saw a mini-tornado through parts of the Sydney metro yesterday and obviously a very significant amount of flood-related calls right up and down that coastal strip."
It comes as authorities issued an evacuation order for the town of Picton south of Warragamba Dam yesterday after the spill and were closely monitoring flood-prone areas of western Sydney.
"As a result of rising flood waters people within the Picton CBD should prepare to evacuate," the NSW SES said.
"Residents should monitor the situation and be prepared to evacuate when instructed to do so."
The dam provides much of the drinking water for Sydney, began spilling over on Saturday afternoon in what experts expected to be the first significant overflow of the reservoir since 1990 although there have been smaller breaches more recently.
"We are in uncharted territory," warned Ian Wright, a water expert at Western Sydney University, who said the rapid urbanisation of the western Sydney area around the Warragamba since 1990 meant its spillover could no longer be reabsorbed by surrounding bushland.
"The urban development adds hard, impervious surfaces, and drainage infrastructure. In heavy rain, this can rapidly generate high-velocity floodwaters," Wright tweeted.
The dam had been at 99.2 per cent capacity earlier Saturday and heavy rainfall was expected for the rest of the weekend.
BOM flood operations specialist Justin Robinson told reporters on Saturday that waters from the spill would combine with river flows from the Upper Nepean and also the Grose River, as well as local tributaries including South Creek.
NSW Premier Gladys Berejiklian said emergency services were preparing for either a one-in-five, one-in-10 or one-in-20 year event.
She has asked residents in the catchment area to be on high alert and to monitor websites in case they were asked to evacuate.
"The window for evacuation is often not a big one depending on where you live," she said.
Berejiklian said the SES was doing its best to predict what may happen in the next few hours and was trying to avoid people being evacuated at night.
There was one lucky save yesterday when a cow washed up onto a beach right near a surf lifesaving club.
Patrons at Old Bar Taree Surf life saving club were shocked by the suprise sight but were quick to spring into action to rescue the unlikely beach visitor.