Emergency services have performed six rescues in NSW in the past 24 hours as heavy rain continues to bombard the state.
Conditions are expected to intensify until midnight as the weather system causing the downpour moves from west to east.
NSW Premier Dominic Perrottet urged people to stay safe, be cautious on the roads and avoid driving through flood waters.
"Don't put your life at risk, your family at risk or our volunteers at risk," he said.
There are 63 flood warnings in place and residents across NSW, including in Sydney, are being asked to stay across their local situations as rivers swell.
Four defence helicopters will come online from 6pm on Saturday in response to a request for extra help from the NSW State Emergency Service.
The agency has received 330 calls for help in the past 24 hours.
Parts of NSW have seen up to 100 millimetres of rain so far, with full dams and saturated catchments meaning rivers are prone to flash flooding.
The Bureau of Meteorology's Jane Golding said the rain would intensify throughout Saturday into early Sunday east of the Great Dividing Range.
It will begin easing by midday, with some sunshine forecast for the start of the week.
"The good news is this system is moving through pretty quickly and we should have a couple of days of reprieve," Ms Golding said.
Major flooding is occurring on the Macquarie, Darling, Culgoa and Lachlan rivers, a risk of inundation is current for multiple inland catchments and forecasters are concerned about the possibility of landslides.
Damaging winds are also likely across Sydney and along the Illawarra coast into Sunday, with peak gusts of more than 90km/h.
The system is expected to blanket the state throughout the weekend, with widespread showers forecast from top to bottom.
Supercars enthusiasts camping at the Bathurst 1000 have been warned of stormy and potentially dangerous conditions, with heavy dumps threatening at Mount Panorama on Saturday and Sunday.
Up to 100mm could drench the tens of thousands of fans attending and potentially trigger flooding along the Macquarie River in Bathurst.
Free sandbags are available in the town, while volunteers are checking in with residents and tourists camping on the river's banks.
Mr Perrottet urged attendees to look out for each other when they headed home on Sunday, with the end of the event likely to see packed roads.
As flood peaks move down already swollen rivers around the state, the BoM has warned of renewed risks for the Gwydir, Namoi, Macquarie and Belubula rivers, Mandagery Creek, the Lachlan and Bogan rivers, Colo River, Wollombi Brook and Lower Hunter River.
NSW SES Commissioner Carlene York urged people to remain vigilant throughout the coming week.
"It is important to remember that the rains will pass and the sun will come out, but the rivers may still be rising," she said.
Australian Associated Press
