The Bureau of Meteorology (BoM) warned persistent rainfall and dangerous conditions would continue on Thursday after the east coast low that battered southern Queensland moved south, submerged parts of Lismore and Ballina, then began to drench Sydney, Wollongong and towns along the coastline on Wednesday.

The weather system had claimed at least five lives in NSW, four of them in Lismore and one on the Central Coast. The body of a man, believed to be aged in his 70s, was found in a flooded unit in South Lismore. In Queensland, nine people have already died and one remains missing.

Residents in affected areas should prepare for the worst, the NSW State Emergency Service said.

"There is a really dangerous weather system that we've got moving south and it's got a really large footprint," a spokeswoman said.

"We know that it could lead to major impacts on construction, power outages, flooding, property destruction and disruption to public transport."

Leave now and stay with friends or family

Residents on the fringes of north-western Sydney at North Richmond were being asked to evacuate their homes on Wednesday evening as the Hawkesbury River continued to climb. The BoM said it could rise to 14 metres on Thursday with major flooding similar to the flood event that devastated the area in March 2021.

Between 9am and 3pm on Wednesday 116mm of rain fell around Wollongong and the Blue Mountains, and across the Illawarra to the Central Coast, with more flood-bearing rain expected overnight and for the rest of the week.

Warragamba Dam, Sydney's main drinking water supply, reached capacity and spilled over before dawn on Wednesday. It feeds into the already-saturated Hawkesbury-Nepean catchment.

Picton residents south of Sydney were told to prepare for an evacuation order, one of seven evacuation warnings and 30 orders in place in NSW, mainly around Ballina and the Northern Rivers region.

Roads and schools closed

Major flood warnings were also in place for the Clarence River at Grafton, Ulmarra and Maclean, the Weir River downstream of Giddi Giddi South and the Richmond River at Coraki, Bungawalbyn and Woodburn.

Numerous other areas around NSW were being told to expect minor flooding and moderate flooding for the Tweed, Georges River, Shoalhaven and Wilsons Rivers.

And just as schools started to settle into the new year living with COVID-19, 147 public schools and 29 independent schools were affected by the wild weather, but conditions were changing by the hour. Many south-east Queensland schools also remained closed on Wednesday.

Across NSW, 661 roads were closed due to the severe weather, including landslides, which stopped traffic on the Princess Highway at Kiama.

NSW SES had received 8,843 requests for assistance between the morning of Tuesday, February 22 and 2pm on Wednesday this week. There were 1,414 flood rescues over the same time period.

In Queensland, the Fire and Emergency Services said it had received 10,200 requests for help over the seven days to Wednesday.

It had been called to more than 600 water-related rescues.

"We come together as a community"

NSW Premier Dominic Perrottet said he was unable to get to Ballina or Lismore due to flooding, but had written to the prime minister requesting emergency assistance. He warned the recovery, which will also affect southern Queensland, could take "months".

"When these difficult situations arise ... we come together as a community," he said. "I've heard stories today of many members of the community coming along, lending a hand, providing support to get the community through. And I think that's incredibly impressive and it shows the true character and the values of our great people."

Among the helpers was a Sikh Volunteers Australia van filled with curries. It made the 22-hour drive from Melbourne to Lismore to deliver food to flood victims on the Northern Rivers.

30 hours of flood-bearing rain

The dangerous weather is being driven by a low pressure system sitting off the mid-North Coast of NSW, senior BoM meteorologist Jordan Notara told ACM.

"This low pressure system is going to slowly track towards the coast and, the anticipation is, that as this low moves closer towards the coast, we will be seeing additional rainfall over the regions," he said.

Mr Notara said the conditions were brought about by the increased humidity in the southern Tasman sea, causing moisture and persistent showers around the central part of the coastline as the system moved south from Queensland and northern NSW.

"We are unfortunately going to see the risk of more rain on top of, obviously, the potential risk of this upcoming 30 hours or so of potential flood-bearing rain.

"So it is unfortunately just going to continue until we start to see a clearance," he said.