Prime Minister Scott Morrison says the Australian Defence Force is readying itself to help deal with the flooding in NSW.
Mr Morrison told parliament on Monday the country was being "tested" by the flooding in NSW and parts of Queensland, and there could be worse to come.
A formal request for ADF help from the NSW government was expected on Monday, he said.
"We understand that this is likely to be for recovery support and cleanup operations including personnel, vehicles and machinery," Mr Morrison said.
It could also involve heavy-lift aerial support.
"The ADF is readying itself for this task that still lies ahead, particularly in the recovery phase," Mr Morrison said
Across NSW, 1400 SES personnel have responded to more than 7500 requests for assistance.
In southeast Queensland, more than 300 SES requests for help have been recorded.
The Bureau of Meteorology has issued a severe weather warning for western and southern Queensland from this afternoon, which could extend to the southeast coast on Tuesday morning.
Some parts of NSW are experiencing the worst flooding in at least 50 years, with evacuation orders in place for 28 areas and a further 16 areas issued with an evacuation warning.
The prime minister said there was a "serious risk still ahead".
"Heavy rainfall is likely to continue up much of the eastern half of NSW and into southern Queensland today and tomorrow," he said.
"Heavy falls will also develop over northern and central inland parts of NSW tomorrow, bringing the risk of flash and significant river flooding to several additional catchments."
Federal disaster recovery payments and allowances have been activated to support those who have been affected.
Mr Morrison said he was grateful there had been no lives lost so far.
