Rainfall is easing across coastal NSW as 15,000 people ready themselves for evacuation and weather authorities warn flood risks are unlikely to abate for several days.
Some 18,000 NSW residents have been evacuated from their homes since last week, with warnings the flood clean-up could stretch beyond Easter.
Premier Gladys Berejiklian on Tuesday said there were several weather fronts, "catastrophic" in their dimensions, impacting large swathes of the state.
"This is a weather incident beyond anything we could have comprehended," Ms Berejiklian said in parliament.
The premier has asked her deputy, John Barilaro, to lead the state's recovery, as he did after the Black Summer bushfires.
People northwest of Sydney have been ordered to evacuate homes amid the downpour as a surge of water flows into catchments, causing rivers to rise.
Major flooding is occurring along the Colo River.
The State Emergency Service ordered about 500 people in 200 homes to get out on Tuesday.
Boats and helicopters were deployed by the SES to help them leave.
A family fleeing flooding on the river needed to be rescued twice after the boat evacuating them capsized on Tuesday afternoon.
Three SES crews were also on board when the boat overturned as it approached the Sackville Ferry Wharf.
People in caravans along a stretch of the Hawkesbury River from Windsor to Wiseman's Ferry have been told to prepare to leave, as have those in the Picton CBD due to rising levels at Stonequarry Creek.
More than 10,000 requests for help have been made around NSW since Thursday, with emergency services performing about 900 flood rescues.
An inland weather system coming across from the Northern Territory is also blighting rural communities such as Grafton and Lismore.
Evacuation warnings persist at Kempsey on the state's mid north coast, while the Hunter, the Central Tablelands and the south coast are in for a drenching.
A major flood warning is in place for the Orara River at Glenreagh and Coutts Crossing.
Warnings of moderate flooding along the Nepean River at Penrith are in place and floodwaters are expected to affect the upper Nepean.
Rain started to ease in coastal areas on Tuesday evening, but the Bureau of Meteorology says conditions will remain severe for inland NSW.
Sunnier skies in coastal NSW will not end flood risks, with rain catchments continuing to flow into bursting rivers.
It will also likely continue to rain on the state's south coast.
"It is very important to remember that even though we'll have blue sky and sunshine returning, flooding will continue and the flood risk will continue," bureau meteorologist Agata Imielska told reporters on Tuesday.
Ms Berejiklian also warned the rivers would keep rising after the rain stopped.
"If you have been asked to be on alert for evacuation, please get together your precious belongings, make sure you are safe and make sure you're ready to leave at very short notice," Ms Berejiklian told reporters.
Two Australian Defence Force aircraft have been made available to the SES on the NSW south coast for search and rescue activities.
Prime Minister Scott Morrison told reporters the government had received a request for 1000 ADF personnel to help with the NSW clean-up.
The federal government said later on Tuesday that $5.7 million had already been distributed in assistance to the flood-affected.
"We want it to be done swiftly and effectively to try and get these communities back on their feet as quickly as we possibly can," Mr Morrison said.
The weather bureau was forecasting widespread falls of more than 100mm across the NSW south coast on Tuesday and up to 300mm in some parts.
Some 280 NSW schools were closed on Tuesday due to the rainfall.
© AAP 2021