Severe thunderstorms will bring large hailstones and a flash-flood risk to inland NSW as heavy rain belts catchments to the east, renewing the flood threat to the state's coastal rivers.
"We're bracing for significant rainfall right across NSW today," Flood Recovery Minister Steph Cooke said on Friday.
Severe thunderstorm alerts have been issued for parts of the Northern Rivers, North West Slopes and Plains and Northern Tablelands.
Storms will bring heavy rain to northern NSW and create a flash flooding risk in Kyogle, Urbenville and Wiangaree on Friday.
Emergency services are keeping a watchful eye on the Gwydir, Namoi and Upper Macintyre rivers on Friday, after heavy rainfall on Thursday led to renewed river rises across the inland catchments.
Severe thunderstorms will bring large hailstones and heavy rain in areas including Moree, Narrabri, Barraba, Bellata, Burren Junction, Wee Waa and Boggabri on Friday.
More than 100mm of rain fell in six hours on Friday at Moree, and moderate flooding is possible by Saturday evening.
Emergency services are continuing their efforts in Moama, the sister town to Victoria's Echuca, which has been the focus of the flood threat in recent days.
The Murray River passed major flood levels late on Wednesday night and is now within 20 centimetres of the 94.77m height of a 1993 flood, the area's second-worst on record.
The bureau expects the Murray to reach around 95m next week, still below the 96.2m height of its worst flood in 1870.
Hundreds of people have been ordered to evacuate Moama and surrounds this week.
"We are very much on high alert," Ms Cooke said.
"Communities have been battered over and over again by natural disasters, particularly since the 2019/20 bushfire season."
Ms Cooke made the comments before opening a temporary housing village in the Northern Rivers town of Coraki, which is providing homes to residents left homeless by flooding in Lismore and surrounds earlier this year.
Meanwhile, western Sydney residents are expecting minor to major flooding to begin on the rising Hawkesbury-Nepean rivers on Friday.
Several suburbs including Windsor, Penrith, and North Richmond have been told to monitor the conditions.
The Hawkesbury-Nepean region has already suffered two major floods this year.
The threat is being exacerbated as widespread showers are forecast for the region on Friday, before a renewed rain-bearing system develops over the weekend.
"Another low-pressure system is set to form over southern NSW and that will drive further showers and storms into mid-next week," senior Bureau of Meteorology meteorologist Jonathan How said.
"Thunderstorms have been quite hit and miss, but some locations have seen more than 100mm (rainfall)."
Major flooding was occurring in the Brewarrina shire, Warren, far western town Tilpa and along the Murray.
The flooding threat comes as the NSW government presses the federal government to share funding for the proposed $1.6 billion raising of the Warragamba Dam on a tributary of the Nepean River.
"This is an important project for the protection of property and lives in western Sydney," NSW Premier Dominic Perrottet told 2GB on Friday.
