The Bureau of Meteorology is warning of severe thunderstorms and heavy rainfall on Tuesday evening in the Northern Rivers, mid-north coast, Northern Tablelands and other parts of the state as far west as Dubbo and Walgett.

Flash flooding could be life-threatening.

The BOM says between 400 and 500 millimetres has been recorded in the northern rivers and on the mid-north coast in recent days.

Meteorologist Agata Imielska said on Tuesday "that's about half a metre of rainfall in the space of about four days".

An evacuation order from the State Emergency Service remains in place from Condong to Tumbulgum and surrounds, with an evacuation warning still current around the Tweed River at South Murwillumbah.

An SES spokesperson said the region has been deemed "a high danger area" and about 1000 properties are affected.

The evacuation order comes after the Tweed River burst its banks near Tumbulgum, with minor to moderate flooding in the area.

There are also flood warnings in place for some communities on the Richmond, Wilsons, Hastings, Orara, Macleay, Nambucca, Bellinger and Kalang Rivers.

Bellingen resident Shelley Rowntree, who lives on a farm just outside the town, said she and her husband had been cut off by flooded roads since Sunday.

Ms Rowntree said 350mm had fallen in three days and it was still raining.

"I hope it stops soon, any more rain and our shed will be under," she told AAP.

The volunteer firefighter says it's a big change from 12 months ago when their property was threatened by bushfire.

"Last year's fires ended in floods. Now here we are again. More extremes, one after the other," Ms Rowntree said.

BOM flood operations manager Justin Robinson said a flood warning was also in place for Kempsey where there was a possibility of moderate flooding on Wednesday.

"There is still an evolving flood situation," he said.

Strong winds will continue on the Macquarie and Hunter Coasts throughout Tuesday and Wednesday.

The SES warned that electricity, phones, internet, water and sewage could be interrupted and people in those areas needed to closely monitor the weather and road closures.

Essential Energy said 2600 homes were without power from Kempsey to the Queensland border.

The SES said residents should monitor the rapidly changing situation in NSW, warning that once floodwater begins inundating the area, roads may be cut, trapping anyone who stays behind.

"If you remain in the area after this time, you may become trapped and it may be too dangerous for NSW SES to rescue you," the SES warned in a statement.

The BOM said 578mm had fallen at Terania Creek on the NSW mid-north coast since Friday.

Meteorologist Ms Imielska says as the low pressure system moves south towards Sydney and the South Coast of NSW it will continue to weaken.

The system combined with king tides to wash away much of Byron Bay's Main Beach on Monday.

On the Gold Coast the weather system also caused massive coastal erosion, with the surf club at Currumbin becoming an island.

A team of 300 SES workers from across the state had been sent to support the northern NSW teams, as well as resources from Fire & Rescue, NSW RFS and NSW Police.

Australian Associated Press