Emergency services urge residents in flood-prone areas of NSW to prepare to evacuate and be cautious while driving, after responding to hundreds of incidents in the past few days.
Heavy rainfall spilled dams and swelled rivers with multiple flood warnings issued.
Residents in part of Lower Portland, east of the Hawkesbury River have been told to evacuate by the State Emergency Service due to rising flooding, before 2am on Sunday with evacuation routes to be closed.
The river may reach the minor flooding level at Sackville and the area may be impacted by dangerous floodwaters, the SES said in a warning issued on Friday night.
People in Camden and Menangle southwest of Sydney, and at Chipping Norton in the city's west, were warned to prepare to flee rising waters, the SES said on Friday afternoon.
Those who remain may find themselves trapped without power, water and other essential services and it may be too dangerous to rescue them, the SES warned.
The SES has responded to 550 incidents since rain began to pound the state on Tuesday, with 50 of those flood rescues.
All 50 of those rescues were caused by people driving through flooded waters.
"Even 10 to 15cm of water, if it's running at a high velocity will cause a car to move," NSW SES Acting Commissioner Debbie Platz said.
"It is extremely dangerous and you do not know what is under that water ... I really urge people if it is flooded stay out."
Premier Chris Minns said resources had been moved into the Hawkesbury-Nepean catchment bordering Sydney's west.
"We're expecting potentially flash flooding ... but riverine flooding may be an issue over the weekend," he told reporters on Friday.
The warnings came after a major dam started spilling after heavy rains pushed it over capacity while some parts of NSW received nearly double their monthly average rainfall.
While the rain is starting to ease across much of Sydney, flood risks remain with the deluge hitting saturated catchments and pushing several other dams beyond capacity.
The flood threat has been heightened further south of Sydney with the surface trough, which has been generating heavy falls, moving south on Friday.
Warragamba dam began spilling over on Friday morning at a rate of about 150 gigalitres of water a day, while inflows were 270GL a day and rising, WaterNSW said in a statement.
It is the third consecutive month the dam has spilled.
The dam supplies 80 per cent of Sydney's drinking water and releasing water to reduce storage levels and mitigate flooding ahead of predicted rainfall is not permitted.
It came as the catchment received 87mm of rain in 48 hours.
A severe weather warning issued by the Bureau of Meteorology advised heavy rain will continue in the Illawarra region and the south coast of NSW on Friday afternoon, as rain eases around Sydney.
As much as 100mm could fall in six hours in some areas, while others have already copped a drenching, the bureau warned.
BOM senior meteorologist Angus Hines said the low pressure systems in the south-east of Australia were set to move away and take the rain with them on Saturday.
"Over the past couple of days some places around southern Sydney and in the Illawarra have seen 200 to 300mm, about two months worth of rainfall in less than three days," he said.
"Because we did see that heavy rain, there are still likely to be some flood warnings in play as these river levels are running really high at the moment on the back of that rainfall."
Moderate flooding is likely along the Hawkesbury and Nepean rivers in Sydney's west and the Georges and Woronora rivers in the city's south.
At Cringila in Wollongong's south, 214mm of rain fell in 24 hours to 9am on Friday, with 204mm at Port Kembla and 156mm at Wollongong.
