The emergency now stretches from the Central Coast to the Illawarra, with 97 evacuation orders and 60 warnings covering 45,000 people - up from the 32,000 affected on Monday.
The majority of orders cover areas surrounding the Hawkesbury, Nepean, Georges and Woronora rivers, all of which are still rising.
Major flooding continues at Windsor, Sackville, Richmond, North Richmond and Wisemans Ferry to the northwest of Sydney.
The Bureau of Meteorology is warning of of flash-flooding and high winds with a gale warning for the Hunter and Sydney coasts.
Wet conditions for the battered coast are forecast for the rest of the week, extending to the northern part of the state, which is still reeling from recording-breaking floods in February, March and April.
State Emergency Service spokesman Ashley Sullivan says the situation remains volatile, with the service receiving 475 calls for help overnight.
The SES performed more than 100 flood rescues - mostly people stranded in cars after driving into floodwaters or those who became trapped in their home as the rivers and creeks rose quickly.
"Certainly with the persistent rain we are receiving, the threat will remain into today and tomorrow," Mr Sullivan told ABC TV on Tuesday.
"Even when it does stop raining, the flood threats will continue," he said
Authorities are particularly concerned about the Hunter Valley over the next 48 hours, as the Hunter River system swells.
Because of the saturated ground, rivers and creeks are rising faster than expected.
The SES is warning people to stay off the roads as many are closed due to flooding and felled trees.
Since the start of the event last week the SES has responded to more than 5000 requests for help.
BOM senior meteorologist Jonathan How said there were widespread falls of from 50 to more than 200mm through some parts of southern Sydney and towards the Illawarra overnight.
"We've seen absolutely incredible rainfall totals, and a number of places have not only broken the daily July records, but the daily annual records, particularly Campbelltown which has recorded its wettest day of any month over the last couple of days," he told ABC TV.
The rain is predicted to ease in the afternoon but there are fears of flash-flooding and authorities are urging people to only travel if essential.
Meanwhile, joint disaster funding has been announced for 23 local government areas in Sydney and parts of NSW as an onslaught of rain continues, forcing the evacuation of thousands of people in flood-hit communities.
With significant rainfall totals over many catchments in the past three days, some areas are expected to approach or exceed flood levels of recent events in March 2021, and February, March and April of this year.
Minister for Emergency Management, Senator Murray Watt, said the federal and NSW governments were working together to ensure affected areas get financial and other assistance as soon as possible.
"We have seen some of these impacted communities being hit by floods for a third and fourth time in 18 months, which is extremely distressing to the residents," he said.
NSW Emergency Services Minister Steph Cooke said significant recovery support would be required to help communities once the major weather event passes.
"While we are still very much in the emergency response phase of this developing weather event, as waters recede we will work with communities to assess longer term recovery needs and ensure appropriate long-term support is provided", Ms Cooke said.
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