Ms Ardern made the announcement in Tuvalu, where she is attending the 18-nation Pacific Islands Forum which starts today.
She said the government was ring-fencing half of its global commitment to climate change-related development, to ensure it went to the Pacific.
The funding will go towards providing infrastructure such as water tanks, better tools for dealing with droughts, floods and coastal inundation, as well as further climate hazard mapping and risk planning.
