As some communities remain cut off due to the large floodwaters and with further rain expected, Mr Morrison said the emergency has been unprecedented.
"These are terrible, terrible floods, these are floods that we have not seen in living memory, in anyone's lifetime," he told Sydney radio 2GB on Monday.
"I can understand the great frustration (that has been) expressed, at the same time, there is an enormous effort that has been put in to get to everywhere that people can get to."
Despite complaints from residents in flood-ravaged communities that not enough defence personnel had been deployed, Mr Morrison said several thousand were on standby to assist the recovery effort.
"There are 2000 who are available to be deployed, and those ADF are continuing to roll in where they've been tasked," Mr Morrison said.
"There are difficulties getting into a lot of these places currently ... that's why they're using the helicopters and other supports."
Federal Agriculture Minister David Littleproud said the government was prepared to send more Australian Defence Force personnel in.
"The states make an assessment about what is the timing that they can be brought in that's safe and they're ... not in the road of those professionals," he told ABC Radio on Monday.
"It is a balancing act, we do try and work with the states and say 'make sure they know that the assets are there ready to go', but ultimately, it has to be (the state's) call."
Agricultural losses alone from the floods are expected to be well into the hundreds of millions of dollars, among them livestock, fruit and vegetables, as well as meat-processing plants, Mr Littleproud said.
Insurance Council of Australia representatives and its members will be in Lismore in northeastern NSW on Monday to assist policyholders. Lismore was badly hit by the floods, which killed four of its residents.
"The impacts in Lismore are incredibly distressing, and we understand the timely nature of getting personnel on the ground as soon as possible to assist policyholders in the claims process," CEO Andrew Hall said.
"We want to make this process as simple as possible for the people of Lismore, who are already suffering tremendous losses as a result of these devastating floods."
The death toll from the devastating floods across parts of Queensland and NSW stands at 18 after the discovery of a man's body in southeast Queensland on Sunday.
As of midday on Friday, insurers had received 67,537 claims related to floods in southeast Queensland and NSW.
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