Parts of drought-stricken NSW have received drenchings, with some regions recording 250mm of rain in the past 24 hours.
Heavy rain and thunderstorms are expected to continue for the next two days with the trough that bucketed rain and caused flash-flooding in Queensland moving south.
Rain has also helped quench nearly half of the bushfires burning across NSW.
On Saturday afternoon, there were 69 bushfires burning - none of which were at "watch and act" or "emergency" levels.
At the same time last Sunday, there were 111 bushfires burning.
Bureau of Meterology forecaster Abrar Shabren said the system which had dumped heavy rain on Queensland had begun moving down into northern NSW.
On Saturday the Mid North Coast, Central Coast and Northern Tablelands regions all copped significant rain.
The Tweed and Northern Rivers regions copped the state's biggest falls, with Clothiers Creek receiving 250mm in the 24 hours to 9am on Saturday.
It was expected to continue over to rain heavily in the state's north on Sunday with flood warnings issued for the Orara and Bellinger Rivers on the North Coast..
A strong wind warning has been also issued for the Byron, Illawarra and Batemans Coast regions,
Rain was then expected to head south on Sunday and Monday.
There are concerns that heavy rain could lead to flashflooding and landslips in parts of the south-east and south coast as it moves down the state over the next 24 to 28 hours.
"It could cause heavy blasts of rain as well which would come with gusty conditions," Mr Shabren said.
"It could be damaging to areas that have had bushfires. Trees that have been damaged could be vulnerable. We could also have run-off of debris, soil and even rocks and that could lead to landslides."
Sydney is expected to receive 5 to 15mms on Sunday along with most of the state except for the west, which is forecast to experience temperatures in the mid to high 30s.