Three people managed to escape the vehicle and make their way to safety when it was inundated at Cooyal Creek at Gulgong, north of Mudgee, on Sunday night.
Police say a 45-year-old male driver and two male passengers - aged 43 and 26 - survived but a third passenger, a woman in her 20s, is missing after also getting free from the vehicle.
The search comes as two weather systems cause more pain for NSW residents in already flooded areas as emergency services prepare more people for evacuations.
There are more than 140 current flood warnings across NSW with almost every corner of the state at risk.
Residents at Lismore in the Northern Rivers region were told to prepare to evacuate on Sunday night amid the prospect of a third major flood there this year.
The Bureau of Meteorology says moderate flooding is now likely along the Wilsons River at Lismore from late Monday morning, with major flooding possible from Monday night.
The bureau is predicting heavy rainfall with possible flash flooding over parts of the Northern Rivers through the morning, with six-hourly rainfall totals between 60 to 100mm possible and conditions expected to ease later in the morning.
State Emergency Services northern zone commander Andrew Cribb said some low-lying parts of south Lismore were already underwater, although the flooding was unlikely to be as severe as the inundation that hit the area earlier this year.
"There are still some concerns ... we are still predicting up to moderate flooding," he told Nine's Today program on Monday.
Moderate rain is expected along the coast and ranges further south into the state's mid-north coast, however heavy rainfall is no longer expected in the area.
Other towns at risk of flooding include Hay, Wentworth, Ballina, Yamba and Maclean.
Meanwhile, a second system is travelling across the border from South Australia, bringing more rain to already saturated parts of the state.
Authorities are pleading with people not to drive through floodwaters with a frustrated premier Dominic Perrottet saying they are tying up resources and risking lives.
Emergency Services Minister Steph Cooke said every corner of the state had a flood warning.
The areas of most concern were in the state's north, with waters rising in places including Moree and Gunnedah.
The Mehi River at Moree peaked at 10.5 metres on Sunday and is expected to remain above the major flood level (8.8m) into Tuesday.
Mayor Mark Johnson said there was a sense of relief on Sunday night when the river started to recede but also "a sense of apprehension about the clean-up".
"The damage is horrific and extensive," he told ABC TV on Monday .
"I went for a fly on Saturday and even the crops that weren't flooded, were laying on the ground from excessive rainfall."
Evacuation orders are in place for Moree, Terry Hie Hie, Gunnedah and Carroll in the state's north, the Riverina town of Narrandera and Mudgee in the central west.
Residents have also been ordered to higher ground at Cummeragunja, Mathoura East, Murray Valley and Moama on the Murray River, where floodwater is expected to peak on Monday.
Two hundred Australian Defence Force personnel have been deployed across the state with more than a dozen helicopters helping with rescue and relief efforts, including three defence choppers.
Natural disaster declarations have been made in more than 40 local government areas, opening councils, residents and businesses for financial aid.
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