He said he admired the solidarity New Zealand showed after the attack, and praised Ardern for helping implement new gun control laws and for urging other world leaders and tech companies to find a way to prevent acts of extremism from being shown online, after the gunman livestreamed his attack on Facebook.

Ardern this week plans to travel to Paris, where she and French President Emmanuel Macron will host a meeting seeking to eliminate such acts from being shown online.

Guterres said countries were not living up to their commitments under the 2016 Paris Agreement to keep the global temperature rise to below 2 degrees Celsius above pre-industrial levels.

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"We are not on track to achieve the objectives defined in the Paris Agreement," Guterres said. "And the paradox is that as things are getting worse on the ground, political will seems to be fading."

He commended Ardern on last week introducing an ambitious bill that aims to make New Zealand mostly carbon neutral by 2050 while giving some leeway to farmers. The bill is expected to come to a final vote in Parliament later this year.

Guterres said Pacific Island nations are on the front line of climate change.

"We cannot allow for runaway climate change," he said. "We need to protect the lives of our people and we need to protect our planet."

Guterres also plans to visit the island nations of Fiji, Tuvalu and Vanuatu. In Fiji, he will meet with leaders and senior government officials from the Pacific Islands Forum. His trip comes ahead of the Climate Action Summit that he plans to convene in September in New York.

AAP