A woman is missing in floodwaters in central-west NSW after a vehicle was swept off a causeway.

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, was missing on Monday after also getting free from the vehicle.

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

There were more than 140 flood warnings across NSW on Monday, 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, facing the prospect of a third major flood there this year.

The Bureau of Meteorology said moderate flooding was 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 of 60-100 millimetres possible. Conditions are expected to ease later in the morning.

NSW 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.

Tweet from @NSWSES

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 NSW Premier Dominic Perrottet saying they are tying up resources and risking lives.

Emergency Services Minister Steph Cooke said every corner of NSW 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 was expected to remain above the major flood level (8.8 metres) 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.”

There are evacuation orders 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.

Across NSW, 200 Australian Defence Force personnel have been deployed, with more than a dozen helicopters helping with rescue and relief efforts, including three defence choppers.

There are natural disaster declarations in more than 40 local government areas, opening councils, residents and businesses for financial aid.

Further flood threat to Victoria, SA

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 said 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.”

One belongs to former policeman Nick Dean. His gas heating and garage have been inundated and the only way in and out of his home is via boat.

“You can imagine the anger with council who put this levee up and thrown us to the wolves,” Mr Dean told 3AW.

“This levees’s made it worse because the waters hit back and bounced back [to his home].”

Tweet from @SA_SES

The Murray River surpassed the 1993 flood level at Echuca on Saturday while the Loddon River at Kerang peaked but the threat is yet to pass.

Floodwaters have receded only slightly and are not expected to noticeably drop for up to a week, keeping the community isolated.

The Bureau of Meteorology warned on Monday severe storms could hit towns in the state’s north, including Echuca and Shepparton, producing heavy rainfall that might cause renewed flooding.

Severe weather warnings were also in place for the Mallee and Wimmera districts down to the Grampians, with the bureau predicting up to 100 millimetres of rain within 24 hours in some areas.

Across the border in South Australia, the SES has responded to calls for help across the Riverland and mid-north districts after heavy rain brought localised flooding and road closures at the weekend.

A flood watch and act warning remains for Stockport, while a flood advice message was issued at 10pm on Sunday for Renmark and Berri due to “severe thunderstorms” that led to flash flooding.

The BOM reported shortly before 5am on Monday that 95 millimetres of rainfall had fallen on Renmark since 9am on Sunday.

-with AAP