Eight flood evacuation orders have been issued for the NSW mid-north coast as wild weather and torrential rain continues to lash much of the state's east.
People in Kempsey were told by the State Emergency Service to evacuate by midnight with floodwaters tipped to pass 6.6 metres on the Kempsey gauge making it likely the levee may overtop.
Evacuation orders are now in place for low lying areas of Kempsey, Macksville, Port Macquarie, the lower Macleay, Wauchope and Rawdon Island, Taree and Wingham.
People are being asked to more possessions above the predicted flood height, take pets, essential items, warm clothes, medicines, insurance documents and valuables with them and stay with family or friends, or head to evacuation centres.
Kempsey recorded 173 mm of rain between 9 am Sunday to 4 am on Monday, and it's not letting up.
Heavy rain is likely to lead to flash flooding and will remain a serious risk for the Northern Rivers and Mid-North Coast on Monday and Tuesday, The Bureau of Meteorology warned.
Risks remain for the Hunter and Central Tablelands districts, particularly as catchments are already saturated.
Overnight, emergency workers conducted 150 more flood rescues and responded to 1500 calls for help, taking the total so far for the weekend so far to more than 10,000.
There are 20 evacuation orders in place running from the Mid-North Coast down to the Illawarra, including Sydney and western Sydney, with more expected to be declared on Monday.
Emergency Services Minister David Elliott said the NSW government was expected to be able to confirm later on Monday the Australian Defence Force would move in to support the SES.
"That will include logistics, obviously, assistance with making sure we make safe our communities," he told Nine.
Mr Elliott said the most critical area was the Mid-North Coast where communities were facing the worst flooding conditions since 1929.
Almost NSW 200 schools will be closed on Monday but with the extreme wet weather continuing, decisions will be made hourly on further closures.
"Safety has to come first," Education Minister Sarah Mitchell said Seven.
Communities along the Hawkesbury River in NSW are also bracing for once-in-a-generation flooding that could displace thousands of residents and disrupt utilities for months.
The BOM expects Monday to bring the worst flooding event to the area northwest of Sydney since November 1961, 60 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 SES 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.
Flooding along the Hawkesbury and Nepean rivers comes after the Warragamba Dam spilled over.
People look on as flood water rises over the New Windsor Bridge on The Hawkesbury River in Windsor on 21 March in Sydney, Australia. Source: Jenny Evans/Getty Images
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.
The BOM's Agata Imielska said the severity of rainfall in greater Sydney could ease on Monday but the Mid-North Coast would continue to be drenched and inland NSW would be pounded by rain.
The NSW northwest slopes and plains are forecast to receive four times more rain in two days than the entire March monthly average.
The federal government's natural disaster arrangements have been activated for 18 local government areas across NSW.
