Around half-a-million people in NSW are subject to evacuation orders or warnings as the focus of the state's unprecedented flood crisis moves south, with Greater Sydney, the Hunter and the Central Coast copping a deluge.
Emergency Services Minister Steph Cooke said on Thursday those regions were facing "treacherous weather conditions", with the next 24 hours critical.
Premier Dominic Perrottet said the floods in the Hawkesbury region "will be worse than they were last year".
Along with the wash-up from the destructive floods in the Northern Rivers, the state was facing "a battle on two fronts", he said on Thursday.
"We do believe that things will get worse before they get better," he said.
"But my message to you is that we will get through this."
The Bureau of Meteorology said rainfall levels could hit a peak of 250mm and warned of life-threatening flash flooding and damaging winds with peak gusts in excess of 90km/h.
Major flooding is expected in western Sydney along the Hawkesbury, Nepean and Georges rivers, Colo and Macdonald rivers at Menangle, North Richmond, Penrith and Windsor, with dozens of suburbs on high alert.
The South Coast is also subject to a minor flood warning for the Shoalhaven and Sussex Inlet.
The State Emergency Service has issued 76 evacuation orders affecting 200,000 people and 18 evacuation warnings have been sent to nearly 300,000 people.
Tens of thousands of people living in Sydney's west, northwest and southwestern suburbs including Windsor, North Richmond, Camden and Milperra, have been ordered to flee to safety with evacuation centres set up in suburbs including Canley Vale and Blacktown.
Charity Save the Children Australia has set up child-friendly spaces at the Canley Vale centre and has also sent teams to northern NSW centres and more than 300 schools across the state are closed because of flooding.
The Nepean River at Penrith will reach nine metres, bringing moderate flooding while the Hawkesbury River at North Richmond will reach 15 metres, bringing major flooding.
At Windsor, the Hawkesbury River will reach 14 metres by Thursday night - two metres above its major flood level.
Residents who endured floods in the Hawkesbury-Nepean region a year ago were told to leave on Wednesday evening after around 600 gigalitres of water flowed over the Warragamba Dam wall, threatening around 130,000 homes in its path.
Endeavour Energy is advising customers in low-lying areas to prepare now for power cuts ahead of rising floodwater levels.
More than 300 properties - mainly along the Hawkesbury River below Windsor - have had power cut.
Further north, thousands of properties remain without power after flooding earlier in the week.
Essential Energy said on Wednesday night it had restored power to about 2500 customers, but 18,000 more were still without power, and crews were unable to get into Woodburn, Broadwater and Ballina.
In Lismore, the clean-up and search of flooded homes continues, with four fatalities confirmed so far.
Two women in their 80s and a man in his 70s were found dead in their flooded homes, while another man's body was found floating down a Lismore street.
A fifth man died on the Central Coast last Friday morning after his car was swept away in floodwaters.
Lismore is also facing shortages of essentials such as food, fuel, fresh water and cash as ATMs run out of money.
The BOM has warned areas on the mid north coast and Hunter region already impacted by flooding could see renewed river rises with thunderstorms forecast across the district on Thursday afternoon.
Abnormally high tides and damaging surf warnings are also in place for practically the entire NSW coastline, with east facing beaches at greater risk.
Coastal erosion is likely and low lying areas could also be affected by tidal flooding.
© AAP 2022