The SES said it conducted about 35 separate flood rescues across Sydney on Wednesday.

About 200 homes around Milperra were evacuated due to forecast flooding of the Georges River. The swelling river was expected to peak at 2.85 metres at about 6pm.

Though the flood was classified as minor by the Bureau of Meteorology, an SES spokesman said the organisation predicted all homes were at risk of being inundated.

Among those preparing for rising waters was Chipping Norton resident Nathan Arnold, who like many others in the area, said he had no intention of evacuating.

As well as the motorcycle and expensive power tools, Mr Arnold had to worry about an anxious alpaca and stubborn sheep.

The asphalt of Davy Robinson Drive was hidden beneath a current of knee-deep water, which had seeped into the garages of homes and was predicted to keep rising into the evening.

In preparation, Mr Arnold was moving his belongings upstairs and finding higher ground for his uncooperative pets.

"If we need to we've got the boat. We can start the motor up and float out of here," an upbeat Mr Arnold said.

Around south-west Sydney several major roads were impassable due to the river flooding.

Cars were left abandoned in rising water, debris was strewn on roads and the river was flowing fast.  Shops and businesses were closing shop and sending employees home early as the flood waters cut off access.

While volunteers were door-knocking in the area and advising people to leave their properties, many seemed unconcerned. Several residents said they had experienced flooding in the past and many of the houses along the river are built on stilts or raised above the ground.

Flood risk for the Georges River at Liverpool was downgraded late on Wednesday, after reaching a peak of three metres, about half-a-metre less than authorities had expected.  

The bureau issued flood warnings for Hawkesbury and Nepean Rivers, Wyong River, Tuggerah Lake, Lake Macquarie, Paterson River and Williams River.

Flood waters were highest at the Colo River at Colo. They had reached a peak of 9.3 metres on Wednesday night and were expected to rise further.

No part of the city was spared from pockets of flooding in Wednesday's heavy rain.

The highest 24-hour rainfall totals recorded in the city were in the north-west and south, where about 130 millimetres were recorded around Hornsby and Engadine.

Dressing rooms at Endeavour Stadium, the home ground of the Cronulla Sharks rugby league team, were flooded with knee-high water.

Water rose above car tyres in Crown Street in Surry Hills at about 7am on Wednesday. At the same time, water had already risen through train stations in the inner-west at Lewisham and Marrickville.

Waters rose as high as the platform at the train station at Bardwell Park in Sydney's south. The flooded station caused major delays on the Airport Line throughout the day. It is the second time in the past year the station has been flooded.