Prime Minister Malcolm Turnbull has declared Australia would invoke the ANZUS security treaty for only the second time in its history in response to any attack by North Korea against the United States.

Mr Turnbull also pushed back against calls - including from former prime ministers Tony Abbott and Kevin Rudd - for Australia to develop a missile defence shield to protect the mainland from the threat of North Korea's nuclear weapons and long-range missile program.

The Prime Minister's commitment to assist the US caps off days of escalating tensions, with US President Donald Trump threatening to unleash "fire and fury" on the rogue state and the North Korean regime warning it would attack the US Pacific territory of Guam.

"The United States has no stronger ally than Australia. We have an ANZUS agreement and if there is an attack on Australia or the United States ... each of us will come to the other's aid," Mr Turnbull told Melbourne radio station 3AW on Friday.