Hundreds of thousands of disaster support payment claims have already been requested in Queensland and northern NSW, as heavy rain heads south.
Prime Minister Scott Morrison - currently isolating after testing positive to COVID-19 - says the defence force is pre-positioned in Sydney and Nowra where flash flooding is expected.
The ADF has so far rescued 91 people during 36 missions in flood-stricken areas of Queensland and NSW.
The prime minister thanked communities for pulling together and supporting each other.
"The ADF are highly active in assisting both response efforts and recovery and clean-up efforts, and there is much planning going on, on that front," he said in an update posted to his Facebook page on Wednesday.
Government Services Minister Linda Reynolds said there have been 145,000 claims for government support so far, 90,000 of which were filed on Tuesday.
The emergency federal support is a one-off payment of $1000 for adults and $400 for children affected by floodwaters.
Senator Reynolds said the number of claims is "of a magnitude beyond" anything the government has seen before in a flooding event.
But she would not be drawn on whether the payment, which has been at the same rate since 2006, should increase.
"At the moment, that's what it is," she told ABC Radio National.
"This is a payment for people who need to buy food and emergency supplies ... it is a payment for people to get through the next few days.
"At the moment, our sole focus is on evacuations and these early stages of the disaster that's making sure people are safe."
The minister confirmed 35,000 people have already received the emergency payment in their bank accounts, as Services Australia works to keep up with demand.
Opposition Leader Anthony Albanese says more needs to be done to help people on the ground who have lost everything in the floods.
"People have struggled to get the support they need and aren't in a position to get a MyGov account and go through the bureaucracy," he said in Brisbane.
"We encourage the federal government to have Services Australia representatives on the ground to make sure Queenslanders and those in northern NSW can access emergency relief they're entitled to."
Senator Reynolds confirmed Services Australia teams would be sent to evacuation centres "as soon as it is safe to do so" and will help people who are without internet or paperwork to make claims.
Meanwhile, Emergency Management Minister Bridget McKenzie has defended the government for not yet using its $4.8 billion emergency response fund.
She says it is a "future fund" for catastrophic events expected in coming years.
"We haven't had to draw on (the emergency response fund) yet because we haven't exhausted our other funding," she told Nine.
"Under the legislation, we can use $50 million of the interest (from the fund) to partner with states around mitigation projects - which we've done - and we've put $150 million towards flood mitigation and coastal erosion."
But Labor senator Murray Watt says none of the mitigation projects given funding by the government has started construction, and nor has any funding gone to disaster recovery.
"We're now in our third disaster season since this fund was first established," he told ABC radio.
"There's not a single disaster mitigation project where construction has actually begun - let alone completed under this fund - which is just a shocking lack of preparation for the kind of floods that we're seeing right now."
Senator Watt said the government was also misrepresenting the amount of money spent on disasters in the past three years by including $13 billion in support spent during the pandemic.
"Certainly (COVID) is a disaster, but the fact that the government has to roll in COVID support payments to bump up their disaster support figures shows they haven't done enough to support people recovering from natural disasters," he said.
East Gippsland in Victoria and northern Tasmania are also expected to be hit with storms in the coming days.