The NSW premier is urging residents to follow safety advice and avoid driving through flooding, after State Emergency Service volunteers had to rescue more than 30 people from dangerous waters overnight.
The SES staged 31 flood rescues between 12pm Friday and Saturday afternoon.
"That is way too high," Dominic Perrottet told reporters.
"Those rescues take place in the main because people aren't following the instructions, they're driving through floodwaters. Don't do that. Follow the advice, that's the best way to stay safe."
More than 500 SES volunteers are on the ground, with 745 requests for help across NSW since lunchtime on Friday.
Residents of low lying parts of the Whittingham, Scotts Flat, Glenridding, Dunolly and Combo areas along the Hunter River are being told to prepare to evacuate.
The SES says they may need to evacuate if flood waters rise further, and they are at risk of flash flooding.
In the central west, Eugowra residents are being told to prepare to evacuate as water levels rise along the Mandagery Creek.
On Saturday morning, SES Assistant Commissioner Dean Storey described a hectic 24 hours throughout the state but particularly in the Upper Hunter.
"That continues to be where our focus is today," he told ABC TV.
"Scone and Muswellbrook were affected by floodwaters over the last 24 hours and will continue to be to an extent today, with the focus shifting downstream."
Major flooding is on the cards in Singleton for Sunday morning, and Maitland is also on alert.
'Large statewide flood risk'
Rain eased on Saturday afternoon, with not much forecast for Sunday.
However, the statewide situation remains volatile, with numerous watches and warnings active following a month of heavy rainfall.
Areas of major concern include along the Namoi River at Gunnedah, in the state's northeast, and the Castlereagh River around Molong in the central west.
"This is quite a large statewide flood risk at the moment," Mr Storey said.
"We are urging all communities and those flood prone areas to be aware of the risk and monitor the local conditions and follow the advice."
Sydney's Warragamba Dam began spilling shortly after 9pm on Friday.
WaterNSW says the outflow volume could peak at a rate of about 60-80 gigalitres per day, just a fraction of levels in March that peaked at 500 gigalitres per day.
"On current projections the spill could continue for up to a week," WaterNSW said in a statement on Saturday, adding "downstream impacts are likely".
A flood watch is in place for the Hawesbury Nepean valley in western Sydney.
Police fashion lasso to save flood victims
The Bureau of Meteorology said some areas of the state were hit with more than 100mm of rain on Friday.
There were major flood warnings for the Mooki River at Gunnedah, the Castlereagh at Coonamble, the Lachlan at Jemalong and the Namoi at Gunnedah, Narrabri and Wee Waa, where it's feared residents could be cut off for more than a week.
Police said a Landcruiser was swept from a small causeway and carried 200 metres downstream by rising waters at Burrell Creek, west of Taree, on Friday afternoon.
Two men waded in to rescue the 65-year-old trapped driver but also became stranded. The trio were eventually hauled to safety by five police officers who fashioned a lasso from a length of rope.
Hunter Valley police also dragged a 52-year-old man from a spillway at Muswellbrook after his Toyota Hilux was swept 400m away by the current on Friday evening.
An RFS helicopter rescued a man trapped on the roof of his car in floodwaters at Caroona on the northeastern Liverpool Plains earlier on Friday.
Mr Storey said it was a good time to stay off the roads.
The Oxley Highway is closed in both directions between Carroll and Gunnedah and the Kamilaroi Highway between Curlewis to Breeza.
At Muswellbrook, the New England Highway is closed in both directions.
In the state's north, severe thunderstorms are forecast to develop around Glen Innes and Inverell on Saturday evening, which could lead to flash flooding.
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