Ms Ardern is pledging $300 million in climate-related assistance over four years, an increase of $100 million.
The prime minister made the announcement in New York where she is attending for the United Nations General Assembly this week along with about 140 other world leaders.
Action on climate change is high on her agenda.
In a speech to the Climate Week conference she said climate change posed a security threat to vulnerable nations including New Zealand's Pacific neighbours.
Ms Ardern said it challenged international legal frameworks.
The extra money will go to projects such as reducing the risk of coastal flooding in Tokelau, storing rainwater in Kiribati and strengthening water security across the region.
The money comes from overseas aid funds which were increased by nearly 30 percent in May's Budget.