Rainfall in Sydney has surpassed the monthly average of 83.6 mm for November, with northern suburbs recording 61 mm of rain in just half an hour.
The bulk of the rain came as Sydney residents were trying to get to work, with at least 12 people needing to be rescued from flood waters despite warnings from authorities.
Two police officers were injured as a tree fell down when they tried to assist motorists in the city's north.
“They are just basically people driving through deep water thinking they can get through,” State Emergency Service spokeswoman Terri Langendam told media.
“Floodwaters can be difficult to judge, turning around and delaying travel is always the best option,” the spokeswoman said.
Due to flooding on the runways, nearly 100 flights at Sydney Airport were cancelled or delayed.
During the 24-hour period until 9:00 a.m. local time on Wednesday, the Sydney Harbor area received 106 mm of rain, most of which fell in the hours around sunrise, Bureau of Meteorology scientist Byron Doyle told Xinhua.
“The highest daily that we have recorded for November was in 1984 which was 234 mm, so obviously it's nowhere near that but it's still quite significant,” the scientist said.
“The brunt of it is kind of over. We are expecting another surge to come through towards the afternoon commute period, but I don't think we will see as much as we have already,” the scientist added.