The wild weather cut power, diverted flights, closed roads, brought down trees and resulted in an unseaonal snow storm in the Blue Mountains.
Residents in the greater Sydney were warned to stay indoors as wild weather lashed the region overnight.
About 30,000 homes are without power and wind gusts of 160kmh have been recorded south of the city. As well, there have been snow storms in the Blue Mountains, the ABC reports.
New South Wales State Emergency Service (SES) spokesperson Phil Campbell said the conditions had been dangerous.
"SES volunteers have now responded to 1136 calls for assistance, 46 of which have been flood rescues," he said.
"The majority of those have been in the southern and south-western suburbs of Sydney and have been for people trapped in motor vehicles, and also several rescues of people from homes."
As well, 50 people were rescued from a train trapped by floodwaters in Sydney's south last night.
Mr Campbell said people should avoid any non-essential travel, with the bad weather expected to continue through the morning.