Morrison said the Federal Government would also invest a further $20 million to lease four additional firefighting aircraft.

The Prime Minister also announced Chinook helicopters from Townsville and other military aircraft would assist, as well as the opening of defence force bases from Adelaide to Brisbane for emergency short-term accommodation.

The Navy's largest amphibious ship, HMAS Adelaide, will sail from Sydney this afternoon to sit off the coast should it be required to help with evacuations.

"They will sail this afternoon, they will be located offshore from the fire-affected areas from tomorrow afternoon," Mr Morrison said.

"The Adelaide is fully equipped for disaster relief and humanitarian aid, is able to operate helicopters, 400 crew, including medical staff, as well as 300 tonnes which have been loaded up in recent days of emergency relief supplies."

More to come.