Executives from Google, Twitter, Facebook and Microsoft met with the leaders of France, New Zealand and other countries in Paris to unveil the "Christchurch Call" of voluntary commitments for online platforms.
"To be honest with you, I do not understand the United States", she added.
She said she hoped it would lead to a "more human internet that can not be used by terrorists for their hateful purposes".
He said the Christchurch Call differed from previous initiatives to clean up the internet, because of the involvement of tech companies and its worldwide appeal.
"New Zealand's Muslim community be attacked in that way, the only answer was to do everything we could to prevent it from ever happening again", Ardern said. According to her, the move "shows the Christchurch Call is being acted on".
It was New Zealand's worst peacetime shooting and spurred calls for tech companies to do more to combat extremism on their services.
Ardern meets with British Prime Minister Theresa May in Paris.
The summit, attended by world leaders as well as representatives from global tech giants, comes amid a growing realisation that social media must be better regulated to prevent it from being weaponised by extremists like the one at Christchurch, who broadcast live video of the massacre on Facebook from a head-mounted camera.
Ms Ardern called the measures a "good first step".
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The group includes 55 funds, including 27 from New Zealand and 28 global funds, and includes Crown-owned investors the New Zealand Super Fund, Accident Compensation Corporation, the Government Superannuation Fund, the National Provident Fund and Kiwi Wealth.
"We welcome the continued momentum provided by support for the Christchurch Call as we work with worldwide partners towards our mutual objectives for an open, interoperable, reliable, and secure internet".
"Tackling these threats also requires technical innovation to stay ahead of the type of adversarial media manipulation we saw after Christchurch", Facebook's vice president of integrity, Guy Rosen, said in a blog post.
"It doesn't say what's the minimum duration and again that wouldn't change the gunman's video on the day because even if they banned him for life it wouldn't make much difference to the people who had seen the video".
They promised investments in "digital fingerprinting" to track and remove harmful pictures and videos, and easy-to-use methods for users to report illicit content.
"Companies like Facebook are becoming more aware and more willing to make reforms than the US, and they're doing it purely on grounds of public opinion", Knott said. "And so we must ensure that in our attempts to prevent harm that we do not compromise the integral pillar of society that is freedom of expression", she wrote.