Prince Charles met the troops at Westport as they took part in a major military exercise being held by the New Zealand Defence Force.
He praised the inclusion in it of a threat to world stability from climate change as "of enormous importance".
Charles and Camilla began their 12-day royal trip on 4 November.
In the exercise troops from countries including the UK, US and France are tasked with bringing back stability to a fictitious Pacific island after a militant group has divided its population along ethnic lines, forcing a group of people on to a peninsula which is then hit by a tsunami.
Charles, who was recently made a Field Marshall of the New Zealand Army, told some of the troops: "One of the reasons I've been trying to go on about climate change for so long is unfortunately it's a threat multiplied.
"I'm glad to see that at last various military people are taking this seriously.
"Because I've always felt the threat is going to come more from mass migration, conflict over scarce resources, sea level rise, a drought, floods - every kind of other.
"The fact that you're practising all this is obviously going to be of enormous importance."
More than 2,000 army, naval and airforce personnel from Australia, Canada, Fiji, France, Papua New Guinea, Tonga, the US and UK have been rescuing mock tsunami victims and carrying out other humanitarian and support work during the exercise, which runs until the end of the month.
Charles, a former Royal Navy helicopter pilot, told the troops that 40 years ago he had been a "small cog" in a military exercise, adding: "But whatever the case, you can always blame me if it goes wrong.
"I'm bound to have caused some awful hold-up just at the crucial moment."
During his visit to the exercise's headquarters Charles climbed into the cockpit seat of a Royal New Zealand Airforce NH90 helicopter used for a number of roles, from supporting troops on the battlefield to carrying out search and rescue duties.
He also met military medical staff in a field hospital and chatted to bomb disposal experts from Canada and New Zealand.
The Prince of Wales has met military personnel from eight countries as he and the Duchess of Cornwall continue their royal tour of New Zealand.