Up to 3000 army reservists and an extra naval ship will join bushfire disaster and recovery efforts, the prime minister says.
Four extra firefighting planes will also be leased to tackle the blazes, Scott Morrison said.
Australian Defence Force bases from Brisbane to Adelaide will accommodate bushfire victims left without somewhere to stay.
HMAS Adelaide will also leave Sydney on Saturday to help with coastal evacuations at the NSW-Victoria border.
Mr Morrison defended the amount of time it took the government to deploy the extra resources despite warnings from previous fire chiefs.
"That was the same advice we received from existing fire commissioners," he told ABC News radio on Saturday.
"I just simply don't accept that."
Defence is poised to set up a national task force to coordinate personnel involved in bushfire assistance across the country.
It will also deploy more planes and helicopters to help with transport and evacuation in bushfire areas.
The federal government will cover the $20 million bill for leasing the firefighting aircraft, with operational costs to be shared with states and territories.
A national recovery agency, similar to that set up during the Queensland floods in 2019, will be established to help with the bushfire crisis.
"The scale of the fires is stretching resources on the ground and there are clearly communities that need additional help and in response to that," Mr Morrison said.
"We have seen this disaster escalate to an entirely new level. This length of season is of course, in many senses, unprecedented."
"The issue that is needed today is boots on the ground, planes in the air, ships at sea and trucks rolling into communities that have been impacted."
HMAS Adelaide will join HMAS Choules and MV Sycamore, which have been evacuating people from the Victorian coastal town of Mallacoota, which is cut off by bushfire.
Defence Minister Linda Reynolds said the deployment of the potentially 3000 reservists to help with recovery efforts was a first.
"The government has not taken this decision lightly," Senator Reynolds said.
"Reservists have always performed a critical part in these call-outs for national disasters here in Australia and overseas."
She said the call-out was compulsory, affecting select brigades, with those already fighting fires in their day jobs or defending their homes exempt.
The reservists will be tasked with helping with evacuations, establishing fire breaks and clearing roads.
Two of the additional four leased aerial firefighting craft would arrive in Australia in seven days, with the other two to be in the country in 14 days.
Federal Labor welcomed the additional resources but continued its calls for a meeting of Australian governments to discuss the bushfire crisis.
"This is a national crisis and a national approach is required," shadow defence minister Richard Marles said in a statement.
The current extreme circumstances meant the large roll-out of defence personnel was completely appropriate, he said.