Radiation experts in Christchurch have been working non-stop since Wednesday night, in response to a simulated nuclear emergency.
The National Radiation Laboratory says the scenario involves a response to a reactor at a nuclear power station in Mexico disintegrating.
The exercise is being run by the International Atomic Energy Agency, and involves about 50 countries.
National Radiation Laboratory group manager Jim Turnbull says New Zealand is participating for the first time, even though it would not be affected by a disaster in the Northern hemisphere.
Mr Turnbull says staff may need to help the government give advice to New Zealanders travelling or living in the region, or send experts to assist with a clean-up.
The exercise will end about midday on Friday.