Prime Minister Jacinda Ardern has opened the second anniversary leaders' summit for the Christchurch Call.
Ardern and French President Emmanuel Macron launched the Christchurch Call in the wake of the 2019 Mosque shootings, seeking to work with governments and tech companies to eliminate terrorist and violent extremist content online.
The summit is being held as an online event this morning.
Ardern said good progress had been made since the call was launched.
"In two years we've done important work together, building our common capabilities to respond to crises. Build our resilience and inclusion in our own communities. And dedicating resources to our common work, including setting up an independent structure for the global internet forum to counter terrorism," Ardern said.
But much more work was needed, namely a better understanding of algorithms and at-risk internet users, and better crisis responses when things go wrong, she said.
Macron echoed Jacinda Ardern's comments, and said the Christchurch Call community also has a fine balancing act to negotiate.
"We also acknowledged that this fight against terrorism cannot be waged at the cost of our values - open societies ... free open and secure internet," Macron said.
Macron welcomed the six new nations who had joined the call, namely the United States, Tunisia, Peru, Estonia, Czech Republic and Croatia.
It was vital that democracies come together to fight extremist content online, he said.
British authorities have removed more than 300,000 items of online terrorist material from the internet over the past decade, according to British Prime Minister Boris Johnson.
Johnson addressed the Christchurch Call summit this morning, highlighting his support for the fight against extremist content online.
"The world wide web is global and it presents a unique challenge to us all in that none of us are protected unless all of us act together. And that's why I support the Christchurch Call for action and why it's such a valuable piece of work," Johnson said.
The United Kingdom had developed and shared technology which could automatically detect if videos had been shared by terrorist groups, he said.
In a statement, InternetNZ said "big steps" were made at the summit.
InternetNZ chief executive Jordan Carter said: "In the last two years, there has been some good progress achieved together. However, it's now crucial that we all improve the ways we are working together - governments, companies, and civil society - if we want to make the most difference.
"The work plan agreed today is an important step in that direction. All the participants in the Call have agreed the principles of working well together, and it's now time to put those principles more fully into practice."
InternetNZ's chief advisor international, Dr Ellen Strickland, said: "The summit today was the culmination of a few weeks of intense collaboration around work plans to take forward this important work, together. The challenge for the Christchurch Call community is now the ongoing commitment to working together and making progress on some of the key areas of work".
The summit endorsed work in four areas over the next year: building the Call's community, transparency, crisis response and algorithms, InternetNZ said.