Millions of Australians are bracing for another day of wild weather amid fears more people will be found dead after the catastrophic floods in Queensland and northern NSW.

Interstate emergency service volunteers are on their way to northern NSW, while Sydney braces for torrential rain that could lead to more inundation.

• Read: TND’s quick guide to flood preparation

The surface trough that developed into a low-pressure system has already delivered hundreds of millimetres of torrential rain that has flooded south-east Queensland and northern NSW.

By Wednesday, the slow-moving system had arrived in Sydney. Flash flooding and dangerous weather is expected all the way from south of Newcastle in the Hunter to north of Eden on the NSW south coast, reaching as far inland as Katoomba in the Blue Mountains.

Near flood-ravaged Lismore, the Ballina hospital was evacuated on Tuesday night, while 20,000 homes were without power.

“Damage is widespread with crews seeing many trees over powerlines, poles washed away, and electrical assets completely immersed in water,” Essential Energy said.

The full scale and cost of the destruction of the disaster remains unclear as many areas are still inaccessible, with about 600 roads cut.

Some 22 members of the Victorian State Emergency Service and 12 South Australian SES members and fire service personnel were headed north to assist on Tuesday.

Victoria SES taskforce leader Justin Navas said boat crews would work in Grafton, Lismore and Casino in the northern rivers to “help out in any way we can”.

Lismore residents are no strangers to floods but the most recent inundation of the town has been worse than expected.

Some 35,000 people have been told to evacuate and many more warned to prepare to leave, while 17 councils in northern NSW have been declared disaster zones.

Residents are finding refuge in evacuation centres set up across the region.

The death toll in NSW rose on Wednesday morning, with confirmation a second woman had been found dead in a South Lismore home on Tuesday afternoon. She was in her 80s.

Another woman in her 80s was also confirmed dead in similar circumstances on Tuesday morning.

Queensland’s death toll rose to nine on Tuesday night following the discovery of a man’s body north of Brisbane.

The victim is believed to be a 76-year-old who had been missing since Sunday night when he was washed away in his car near Glen Esk.

The clean-up has begun in Queensland, where “mud army” volunteers are rolling up their sleeves to help.

The Bureau of Meteorology has warned, however, that more “severe weather” will return, disrupting the region’s recovery.

“We are looking at a return for showers and storms late Wednesday into Thursday and Friday,” BOM’s Jonathon How said.

“We could see localised heavy falls of 50 millimetres to 100 millimetres each day, as well as damaging winds and small to large hail.

“Very much, the message to those people in south-east Queensland – the danger isn’t over just yet.”

Tweet from @bne_lordmayor

Billions of damage

The damage bill is estimated to run into billions of dollars, and insurers have already received 31,000 claims from south-east Queensland and northern NSW.

Brisbane Lord Mayor Adrian Schrinner urged people to enlist for the “mud army 2.0” to help clean up in the state capital, where there is a major flood after 795 millimetres of rain in just three days.

With more than 15,000 homes and businesses damaged, many Brisbanites are keen to pitch in again like they did with the first volunteer effort after floods 11 years ago.

“I have revived the renowned mud army from the 2011 flood so we can co-ordinate the clean-up together and ensure people don’t get left behind,” Cr Schrinner said.

“If you helped out in 2011 or have just heard the stories about the heroic efforts of hundreds of Brisbane locals I am urging everyone willing and able to sign up to get involved.”

The Salvation Army and Foodbank Queensland are also appealing for donations to flood appeals in support of affected communities.

More financial support is on the way. The state government has announced hardship grants on top of the Commonwealth’s relief payment, with $180 per person and up to $900 for a family of five or more on offer for flood-hit residents in the Brisbane, Logan and Noosa regions.

RACQ said it was ramping up its response after receiving more than 6000 insurance claims.

Snakes and virus in floodwaters

Public health experts and the state government have warned Queenslanders to stay away from floodwaters during the clean-up.

Epidemiologist Hilary Bambrick said everything from infectious diseases to snakes could potentially lurk in flooded areas.

“Flood water is unpredictable and also contaminated,” she said.

“There’s the potential of biochemical contamination, the debris and potentially snakes – people definitely shouldn’t be jumping in the water for a swim.”

Queenslanders have also been urged be aware that mosquito-borne illnesses will flourish in standing water.

The state government said Ross River virus and malaria could be spread by mosquito bites. Japanese encephalitis virus – which can cause fever, headaches, rashes and convulsions – has also been detected recently in the region.

“Using insect repellent, wearing loose clothes to cover arms and legs and wearing closed-in shoes can significantly increase protection against mosquito bites,” chief health officer John Gerrard said.

Queensland still at risk – and looters are striking

The Port of Brisbane is still closed but most schools will reopen on Wednesday.

Only about 80 will remain shut, down from 550 on Tuesday.

In Gympie, north of Brisbane, flood water filled the Bank of Queensland branch to the ceiling as the Mary River peaked at 23 metres on Monday.

Other businesses on the town’s main street also went under.

By Tuesday, water had receded enough for owners and staff to inspect the damage.

“It’s going to be a complete rebuild at this stage,” BOQ manager Jellina White said.

“Even though it’s a bomb site, at least we sort of can get in and feel like we’re actually doing something at the moment.

“We put everything up as high as we can and then for it to go to 23 [metres]… pretty much just everything went underwater.”

On the Fraser Coast, Maryborough is cleaning up after the Mary River peaked at 10.3 metres, a metre below the flood levee, on Monday night.

It was the city’s second major flood in two months. But this time the CBD stayed dry after it was inundated in January when an underground stormwater valve failed, sending water up through drains.

Local MP Bruce Saunders said there was an “eeriness” as residents waited for the river to rise. But volunteers were already out cleaning up during the “resilience phase” on Tuesday.

“The community spirit here, to get the city back up on its feet, is second to none,” Mr Saunders said.

In Ipswich, more than 150 residents remain stranded in low-lying pockets of Goodna as floodwaters slowly recede.

Councillor Paul Tully said some people remain trapped without electricity or food. Boats were the only way in or out.

He said reports of looting had infuriated Goodna residents who were forced to evacuate.

“Sadly we have had looters. They’ve broken into cars and people’s homes before people even get a chance to look at the damage,” Cr Tully said.

Kate Smolders, who evacuated her flooding Chelmer home with her two children on Sunday, said west Brisbane locals were looking after those affected.

“People are checking in on each other, making sure they are safe and out of their homes, they are really rallying around each other,” she said.

-with AAP