Emergency services were called to the Coopers Creek Canal at Wentworthville on Tuesday morning after reports a body had been sighted in the water.
Police had earlier issued an appeal to find 67-year-old Hemalathasolhyr Satchithanantham and her 34-year-old son Bramooth after their Mazda 3 was found in the stormwater canal on Monday afternoon.
An operation is under way with underwater specialist police resources, police divers and the NSW State Emergency Service.
It comes as up to 80,000 people across NSW are subject to evacuation orders as the flood crisis continues to wreak havoc across the entire coast.
A low pressure system off the mid-north coast has brought torrential rain to the Hunter and Greater Sydney regions and is moving towards the south coast.
The intense rain is causing minor to major flooding from the Queensland border down to the Victorian border.
The SES issued evacuation orders to 60,000 people in 13 suburbs across Sydney's southwest and west along the Georges River overnight.
There are now 54 evacuation orders across the state, as well as 16 evacuation warnings and multiple flood warnings, current for vast swathes of NSW.
SES Commissioner Carlene York said the primary areas of concern were Kempsey, Georges River, the Hawkesbury Nepean River, Wollongong, Shoalhaven, St Georges Basin and Sussex Inlet.
"It's very dangerous out there. There's a lot of water on the roads and it's prone to flash flooding as the heavy rains come," Ms York said.
The SES received more than 2500 calls for help in 24 hours and undertook about 200 flood rescues, mostly in Sydney.
Sydney has endured 16 consecutive days of rain and no reprieve from the deluge is expected until Wednesday and no sign of sunshine until Thursday.
The Bureau of Meteorology is warning saturated soil and swollen rivers could lead to landslides and flooding with rainfall of up to 200mm possible in Sydney's west and southwest.
Wind gusts of up to 90 km/h are forecast, stretching south to the Illawarra region into Wednesday.
The bureau's Dean Narramore said widespread heavy rain overnight brought "devastating flash-flooding to some suburbs".
"It was a dangerous night through parts of southern and southwestern Sydney," he said.
"Travel is definitely dangerous today not only because of rainfall ... Tonight we'll see possible trees and power lines down and landslips and flooding of roads.
"It's still dangerous times out there."
There has been 100mm to 200mm of rain in the past 24 hours.
People in Camden were told to leave on Monday night after 80mm of rain fell and the Nepean River flooded.
The SES later issued evacuation orders for Chipping Norton, Georges Hall, Picnic Point, Pleasure Point and Sandy Point as well as parts of Holsworthy, East Hills, Milperra, Moorebank and Warwick Farm.
People living in parts of Emu Plains, Penrith and Mulgoa in Sydney's far west were told to prepare to evacuate.
Major flooding is occurring on the Macleay River, with parts of Kempsey in the north at risk of being inundated.
There is minor to moderate flooding in the Upper and Lower Hunter and major flooding on the Georges River in the Liverpool area.
The SES is warning river levels could rise along the Nepean and Hawkesbury rivers, potentially bringing "deep and dangerous flooding".
Major flooding is occurring at Menangle, North Richmond, Wisemans Ferry and Putty Road.
Sydney Trains is asking commuters to avoid non-essential travel and allow extra travel time as it undertakes inspections to ensure the rail network remains safe amid the deluge.
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