More drenching rain is expected to follow the severe and damaging thunderstorms that have battered parts of Sydney and surrounds.
The State Emergency Services responded to about 200 calls for help during and after storms and some hail pelted Sydney, the Blue Mountains and Central Coast on Tuesday night.
Most of the calls were for storm damage on the Central Coast and Sydney's western suburbs.
Widespread rain is expected on the South Coast and in the southeast in the next 48 hours.
"Probably the area of concern is really around the flash-flooding risk, people driving through floodwaters or being caught in floodwaters," SES Assistant Commissioner Nicole Hogan told the Nine Network on Wednesday.
"If you come across floodwaters, please take an alternative route. Our volunteers have been working tirelessly since November 10 with the flooding in the west of the state.
The Bureau of Meteorology also issued a strong wind warning for the Sydney coast and Illawarra coast on Wednesday.
The SES was also called to three rescues overnight in flood-affected areas as a month's worth of wet weather continues in soaked catchments.
One woman had to be rescued in Casino in the northern rivers area, when a flash flood went through a campsite, and another person was rescued from a car at Rocky Creek near Narrabri.
An SES spokesman said there were about 300 SES volunteers helping in flood-affected communities and planning was under way to maintain a presence in western NSW until February.
"We are dealing with very wet catchments and low systems coming through bringing thunderstorms and heavy rainfall," the spokesman said.
Slow-moving floodwaters in the west were coming down from Queensland and continual rainfall is predicted across some of those areas.
"So we are predicting that floods in western NSW will continue for a couple of months," the SES spokesman told AAP on Wednesday.
Numerous homesteads in western NSW and towns including Mungindi - which straddles the Barwon River on the Queensland border - are in for a soggy Christmas, the SES spokesman said.
"We are expecting ... as that floodwater moves downstream there will be communities, townships and rural properties that will be isolated moving into Christmas," he said.
The BOM has issued a warning for parts of the northern tablelands with severe thunderstorms likely to produce heavy rainfall that may lead to flash flooding on Wednesday, and likely impacting Glen Innes, Jackadgery and Emmaville.
Multiple rivers across the state are still flooding, with waters expected to remain high for weeks.
Flood warnings are in place for much of the state's inland river system, including the Namoi, Macquarie, Bogan, Lachlan, Murrumbidgee, Warrego, Paroo, Barwon, Macintyre and Weir rivers.
With the forecast weather expected to wreak more havoc, renewed river level rises and flooding is possible from Wednesday across the Upper Macintyre, Gwydir, Castlereagh and Bellinger rivers.
Australian Associated Press