New Zealand could avoid responding with military support if North Korea launches an attack against the United States.
Australian Prime Minister Malcolm Turnbull says Australia will come to the aid of the US because of the promises made in the ANZUS treaty.
"In terms of defence, we are joined at the hip," Mr Turnbull told Australia's 3AW radio on Friday.
But New Zealand and the US are no longer linked in the three-way pact because of disputes over nuclear-armed and nuclear-powered ships.
However, both remain tied to Australia under the agreement, which came into effect in 1952.
Prime Minister Bill English is expected to address the issue at a press conference later on Friday, while Foreign Minister Gerry Brownlee has also been approached for comment.