Military brass from China, the US, Australia and New Zealand convened at SkyCity to simulate the evacuation of a Pacific island.

The scenario was part of a "table top exercise" organised and hosted by the NZ Defence Force at the casino's Auckland convention centre.

But Green MP Golriz Ghahraman has questioned why the exercise needed to be held at the casino convention centre rather than at Defence facilities.

The multi-national military exercise cost $16,000 and ran during the last week of August.

New details about the exercise, termed Cooperation Spirit 2019, have emerged after Stuff obtained a trove of documents under the Official Information Act.

Fifteen NZ Defence Force personnel were deployed to the exercise.

They were joined by a handful of representatives from the Australian Defence Force, the US Military and the People's Liberation Army (China).

Near the top of the agenda was a "table top exercise" centred on a scenario where a natural disaster strikes the fictional fictional nation of Becarra in the south-west Pacific.

The unspecified disaster was so severe it forced the evacuation of an entire island.

A subsequent a scenario in the next table-top exercise shows things going from bad to worse in Becarra.

Large numbers of refugees were arriving at a camp, where the situation was grim.

Reports of abuse, sexual assaults, forced prostitution and child trafficking were rolling in from a camp for displaced people.

Participants were asked how to deal with complaints of abuse and gang activity at the camp.

Green MP Golriz Ghahraman, the party's defence, security and intelligence spokesperson, said the Greens welcomed the Government's re-orientation of Defence capability towards disaster relief, environmental monitoring and climate action.

"Exercises like this are a part of that work."

But she was unsure why the meeting was held at SkyCity.

"Defence have their own facilities in in the region that can accommodate such events at a far lower cost."

"The aspect of Defence spending which has been an enormous cost to successive governments, is the billions of dollars spent on war making vessels and technologies."

The Green Party would prefer to see that funding directed to core government services at home or refocused on aid and environmental protection, Ghahraman said.

A Defence Force spokesman said Auckland was chosen for its ease of access for international participants.

SkyCity was used because it is a "central, secure location, where the accommodation and conference facilities are connected," the spokesman said.

Defence analyst Paul Buchanan said the exercise was a sound example of military diplomacy in action.

The US, China and Australia all had the airborne and naval "heavy lift capability" required to move large numbers of people off a small island quickly, something New Zealand lacked, he said.

It was the first he had heard of the exercise, but he was pleased to hear the four nations were jointly preparing for disasters in the Pacific, set to become more frequent and severe with climate change.

The exercise reflected mounting concerns in militaries the world over about climate change, he said.

"One thing that's interesting is that in policy debates in virtually every western country, and in China, the military does not question the science of climate change.

"It's politicians and non-military people who are climate change deniers.

"The US is a perfect example of it, they have an idiot in the White House but the US military has stepped up to the plate."

Buchanan said he was surprised the French military were not invited to the exercise given its strong presence in New Caledonia.

The NZ Defence Force did not respond to requests for comment on why the French missed out on an invite.

In Buchanan's view, the $16,000 cost was surprisingly low.

"A drop in the bucket."