The defence forces would grow by 18,500 personnel to 80,000 over the 18-year period, at a cost of some Aus$38 billion (US$27 billion), the prime minister said at an army barracks in Brisbane.

Morrison, who is expected to call a general election in May, told a news conference it was the "biggest increase in the size of our defence forces in peacetime in Australian history".

He said the military build-up was a recognition by his government of the "threats and the environment that we face as a country, as a liberal democracy in the Indo-Pacific".

Australia announced in September it would acquire nuclear-powered submarines under a new Australia-Britain-US defence alliance, AUKUS.

Morrison said some of the new troops would be supporting the future submarine fleet.

Australia says it plans to arm the submarines with conventional weapons but has yet to decide on the details of the programme, including whether to opt for a fleet based on US or British nuclear-powered attack submarines.

Forged at a time of growing Chinese influence in the Pacific region, the AUKUS alliance would make Australia the only non-nuclear weapons power with nuclear-powered submarines, capable of travelling long distances without surfacing.