The group -- which includes the former chief of the Australian Defence Force, Admiral Chris Barrie -- used an open letter to call on Australia's political leadership to make climate "an immediate security priority" ahead of federal elections expected in May.

The defence veterans and security experts pointed to the 2019 "Black Summer" bushfires and the floods that have recently devastated eastern Australia as climate disasters that required "major peacetime mobilisations" of Australian troops.

Australia's government faced intense criticism after widespread flooding earlier this month, with affected communities denouncing the deployment of army and reserves as being too slow to aid rescues and recovery.

"Australia has no credible climate policy, leaving our nation unprepared for increasingly harsh impacts," the letter read.

The comments echoed criticism levelled this week by United Nations Secretary-General Antonio Guterres, who singled out Australia as a "holdout" for failing to define meaningful near-term measures to cut fossil fuel emissions.

Senior figures in Australia's conservative governing party dismissed Guterres' comments.

"The chattering classes of the UN can say what they want," communications minister Paul Fletcher said, defending the ambition of Australia's emissions reductions compared with the United States, Canada and New Zealand.

One of the world's leading fossil fuel exporters, Australia last year set a goal to reach net zero emissions by 2050 but has not increased its 2030 targets despite coming under intense pressure to do so during the Glasgow climate summit.

In the run-up to Australia's elections, the government has been burnishing its defence credentials, including an announced expansion of the defence forces by nearly a third by 2040.

But the former defence leaders argue in their open letter that climate and security are inextricable, calling on politicians to "commit to mobilising the resources necessary to address this clear and present danger".