Hundreds of residents across Sydney's south and south-west face a sleepless night as a number of evacuation orders are still active.
The most recent was issued just after 6pm for residents in parts of Camden.
They have been given until 10pm to leave their homes.
While the deluge that sparked flash flooding on Thursday and drenched large swathes of NSW's coast has eased in some parts, it was expected to pick up again overnight.
Earlier on Thursday residents in Chipping Norton were also ordered to leave, with many stranded after rising waters closed bridges and roads, bringing traffic to a standstill.
Locals told the ABC that not knowing how deep the water was going to get was "worrying".
"I've lived here since 1980," resident Muriel Enright said.
"Supposedly [it's a] one-in-50-year flood area and now it's once a month.
"We're waiting to see if we can go across. If it gets a little bit deeper they can maybe get a boat in and we can get in to get other things that we need.
"The notification from the SES said to evacuate by 3pm or 3:30pm, but it's been cut off since 1pm."
Parts of Wallacia, near Warragamba Dam, and Camden were subject to evacuation warnings as of 5pm.
Bureau of Meteorologist (BOM) senior hydrologist Ailsa Schofield said heavy rainfall would persist for the rest of the day across the Hunter, parts of the Central Coast, Greater Sydney, the Illawarra and South Coast.
The heavy rain is predicted to ease overnight, but showers will continue on Friday.
And the wet weather is set to hang around, with the La Niña event expected to continue until the end of April, Ms Schofield said.
NSW SES Acting Commissioner Daniel Austin said the organisation had responded to 680 requests for assistance, including 25 flood rescues over the past 24 hours.
Mr Austin said the most serious rescues were caused by flash flooding in the Sutherland Shire and Illawarra.
"We've seen exceptionally sharp, short bursts of rain that have created significant flash-flooding events," he said.
He said several schools had closed in the Illawarra due to the downpour.
People leaving the city for the school holidays — which begin for most students this weekend — are being warned to drive carefully over the coming days.
Earlier, people living in low-lying areas of Woronora and Bonnet Bay, in the Sutherland Shire, were given until 11:30am to evacuate.
The evacuation warnings for those areas were issued at about 5am Thursday morning due to rising water levels in the Woronora River.
Woronora resident Linda Janssen, whose property backs onto the river, said she had "never seen it run this fast before".
"[I'm] a little nervous," she said.
"Our property is up quite high … for those properties that are a bit lower, it's a real worry."
In Kogarah, flash flooding inundated the Princes Highway at about 3am Thursday morning, and some residents of an aged care home were evacuated during Wednesday night as water entered the building.
Oil and diesel have also been spilling from the Caltex refinery at Kurnell after a pump failed at the facility.
The SES said several roads had been closed and motorists should avoid the area.
Sydney surpassed its average annual rain total already this year, after posting its wettest day of 2022 in the 24 hours to 9am on Thursday.
More than 114 millimetres of rain was recorded in the gauges at Observatory Hill in the CBD on Thursday morning.
Torrential rain fell in parts of the city overnight, including 107mm at Cronulla Bowls Club in the three hours to 1:10am on Thursday morning.
There was also 107mm of rainfall recorded in Little Bay in just six hours.
Earlier on Thursday, flooding stopped traffic closing roads in Chipping Norton, Menangle, Narrabeen, Mona Vale and Oxford Falls.
Residents were encouraged to avoid the area, with social media videos showing cars attempting to cross floodwaters in Manly's CBD.
On Wednesday, the BOM issued a severe weather warning for an area stretching from Newcastle to past Bega in the state's south.
