Two fresh weather systems are closing in on NSW, one expected to dump as much as 200mm of rain, prompting warnings of a "very dangerous" 48 hours ahead.
The latest evacuation orders have been issued for Moree as a major flood peak looms on the Mehi River, a tributary of the Gwydir River, threatening to surpass a 10.87m high mark recorded 67 years ago.
In all, there are 120 flood warnings current around NSW, 20 of them at emergency level.
Premier Dominic Perrottet pleaded with people to avoid driving through floodwaters, pointing to how the rescue of one motorist had recently tied up 20 emergency services volunteers.
"That is taking resources away from our emergency services and importantly, you are risking their lives," he said on Sunday,
The state's SES had conducted 34 rescues and responded to almost 400 requests for help over 24 hours as of Sunday afternoon.
A man in his 30s died in a suspected drowning on Saturday at West Ballina, on the far north coast, while two men stranded in vehicles in the Southern Tablelands centre of Yass were rescued overnight.
Emergency Services Minister Stephanie Cook said there was a flood risk in "every corner" of NSW.
"We are facing a very dangerous 48 hours across NSW," she said.
One weather system is entering NSW from South Australia, bringing fresh rain, while another is hovering at the coastal Queensland border, which has the potential to dump up to 200mm on the already saturated Northern Rivers region.
Authorities say renewed thunderstorms have impacted multiple flood-affected communities along swollen rivers.
Most are in areas surrounding Moree, Gunnedah and the neighbouring village of Carroll on the northern Namoi River, the Riverina town of Narrandera on the Murrumbidgee and Moama on the Murray River.
The Bureau of Meteorology expects heavy rain over the state's northeast from Sunday morning, affecting Lismore, Grafton, Casino, Kyogle, Yamba and Maclean.
Falls of up to 150mm in six hours were possible in some areas.
The bureau's Jane Golding said the system at the NSW / Queensland border was an "evolving risk" and causing meteorologists concern.
"We will have to see how much rain the system produces," she said.
SES Commissioner Carlene York told people to follow evacuation orders.
"It is better to be inconvenienced for 48 hours and go back when we say it is safe," she said.
Crews will be performing rapid damage assessments to quickly give residents the green light to return.
Mr Perrottet said the flood's impact on the state's coffers was "difficult" but NSW had been in a good position before the COVID-19 pandemic to handle multiple crises.
"The NSW budget is not an end to itself, it is there to help families and people right across NSW," he said.
Two hundred Australian Defence Force personnel have been deployed in Dubbo, Moree and the Northern Rivers, with two additional ADF helicopters ready for night rescues.
Specialist swift-water rescue crews have also been dispatched to the flood-threatened north while others are in place on the Macquarie River, at Dubbo.
