Drenching rain in Sydney is forecast to continue into next week after some areas were inundated with more than a month's worth of precipitation in 24 hours.
The deluge caused flash flooding in parts of the city, prompting hundreds of requests for help to the NSW State Emergency Service on Tuesday and Wednesday.
Emergency Services Minister Steph Cooke said on Wednesday that the SES received 1323 calls in 24 hours with 40 children being evacuated from a childcare centre in Marrickville, in Sydney's inner west.
She said the majority of requests concerned leaking roofs, flash flooding on roads and debris.
Fire and Rescue also responded to 114 storm-related incidents in the past 24 hours, Ms Cooke said during parliamentary question time.
"Looking into the future we know that New South Wales and Australia will continue to face significant events like those we have been experiencing these past three years," she said.
Parts of the state's northeast may receive 100mm of rain over the next four days, the Bureau of Meteorology said.
More torrential rains are expected across the northeast of the state and southeast Queensland.
Flood warnings have been issued for Tweed, Brunswick, Wilsons, Richmond, Orara, Bellinger and Nambucca Rivers.
BOM's radar showed heavy falls with thunderstorms leaving many Sydney suburbs recording more than 100mm of rain on Tuesday.
Many roads are flooded and ferry services have been cancelled between Parramatta and Sydney Olympic Park on Wednesday due to flooding and debris on the swollen Parramatta River.
The Sydney suburb of Marrickville was hit by the heaviest falls, recording 169mm of rain in just 24 hours.
Sydney Airport recorded 137mm, Rose Bay in the inner east 121mm, while Canterbury in the southwest reported 119mm.
More than 100mm was recorded in a number of locations around western Sydney including Bankstown, Lidcombe, Auburn, Guildford, Toongabbie, North Ryde and Castle Hill.
On the Central Coast, Wyong recorded 160mm of rain and Kulnura 102mm.
Weatherzone, a weather monitoring service, said "wet and stormy weather will persist into Thursday, Friday and possibly Saturday" across northeast NSW and southeast QLD, due to an upper-level trough passing over the region.
It said the downpour will record between 200 to 500mm in total in the coming days in some areas.
The deluge comes after NSW experienced a wetter than usual summer in the midst of a La Nina weather pattern that's predicted to stretch into autumn.
