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 getting free from the vehicle.

The search comes as two weather systems cause more pain for NSW residents in already flooded areas and emergency services prepare more people for evacuations.

There are more than 140 flood warnings across NSW with almost every corner of the state at risk, with 550 State Emergency Services volunteers in the field and reinforcements from WA due to arrive on Monday.

Flooding is set to peak in the Murray River at Echuca, where dozens of houses built along the banks have been swallowed up by water.

Flood walls have so far protected the centre of town from the worst of the disaster after heavy rain set in overnight.

But properties on the so-called wrong side of a levee constructed over the past week to save major infrastructure have started to flood.

“Our house is surrounded by water,” resident Julie Golledge told AAP on Monday, when about 20 centimetres of water had already seeped into her garage.

“There are a number of houses that do have water flowing in them because they’re lower lying compared to us.”

Residents at Lismore in the NSW Northern Rivers region were told to prepare to evacuate on Sunday night amid the prospect of a third major flood in eight months.

Some low-lying parts of south Lismore are already underwater, although the flooding is unlikely to be as severe as the inundation that hit the area earlier 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 of between 60 to 100mm possible before conditions ease.

Emergency Services Minister Stephanie Cooke said authorities were keeping a “very, very close eye” on Lismore and the wider region.

“We all know how much those communities have been through this year,” she told ABC TV.

There are also concerns about Moree in the state’s north, where the town is experiencing its worst flooding in a decade.

Farmers in the agricultural hub were just weeks away from harvesting crops, which are now destroyed.

“It’s heartbreaking. There’s no doubt the damage and devastation through that region will be deep and widespread,” Cooke said.

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 apprehension about the clean-up.

Other towns at risk of flooding include Hay, Wentworth, Ballina, Yamba and Maclean.

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.

Meanwhile, a second system is bringing more rain to already saturated parts of the state.
Residents have also been ordered to higher ground at Cummeragunja and Mathoura East on the Murray River, where floodwater is expected to peak on Monday.

Authorities continue to keep a close eye on the southern border town of Moama, with major flooding expected when the Murray River peaks at 94.9 metres on Monday – higher than the 1993 flood.

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.