World leaders and heads of global technology companies have pledged at a Paris summit to tackle terrorist and extremist violence online in what they described as an “unprecedented agreement”.

Wednesday’s event, two months to the day since the Christchurch massacre in New Zealand, drew up a “plan of action” to be adopted by countries and companies to prevent extreme material from going viral on the internet.

Known as the Christchurch Call, it was organised by New Zealand’s prime minister, Jacinda Ardern, and the French president, Emmanuel Macron, in response to the attack on the Christchurch mosque on 15 March in which 51 people were killed.

The gunman, a 28-year-old Australian, livestreamed the attack on Facebook from where it was shared online around the world. The footage was picked up by some international media outlets who initially published excerpts of the video and links to the gunman’s extremist “manifesto” before quickly dropping them in the face of political and public outrage.

Macron and Ardern met ministers from G7 nations and leaders of internet companies including Google, Facebook, Microsoft and Twitter. Facebook’s CEO, Mark Zuckerberg, did not attend.

The initiative calls on signatory nations to bring in laws that ban offensive material and to set guidelines on how the traditional media report acts of terrorism. However, as a voluntary initiative it is for individual countries and companies to decide how to honour their pledge.

Facebook Twitter Pinterest At the table, from left: Jean-Claude Juncker, Theresa May, Norway’s Erna Solberg, Senegal’s Macky Sall, Jacinda Ardern and Emmanuel Macron. Photograph: Charles Platiau/pool/EPA

Britain, Canada, Australia, Jordan, Senegal, Indonesia, Norway and Ireland signed the pledge, along with the European commission, Amazon, Facebook, Google, Microsoft, Twitter, YouTube, Daily Motion and Quant.

France’s Elysée Palace said Germany, India, Japan, Holland, Spain and Sweden had expressed support for the Christchurch Call.

The US has reportedly refused to sign up because of concerns about freedom of speech.

At a press conference after the Paris meeting, Macron made reference to recent attacks in Sri Lanka and the killing of two French soldiers by terrorists in Burkina Faso.

He said: “Our aim is simply that what has happened in each of these places never happens again. Christchurch was not just an abject terrorist attack, it was the transformation once again of the internet into a crazy propaganda machine used for the fracture of our society.

“The war of everyone against everyone else [is] an objective of extreme right and Islamist terrorists. The objective of our joint initiative is to enlarge the field of action. We have decided to act.”

Ardern said the Christchurch attack was “truly unprecedented in its use of social media and subsequent spread of the terrorist’s message. Fifty-one men, women and children from the New Zealand Muslim community were killed, and were killed online. Initially the live stream was watched by only a few hundred people but it was then shared and spread online at such a pace that YouTube recorded one upload per second on their platform in the first 24 hours.”

She added: “Never have so many countries and tech companies come together in reaction to such an attack to work together to use new technology and develop new technology so our communities are safer.

“Today must be day one of change. The Christchurch Call is a roadmap for action. It’s a nine-point commitment that I hope will bring lead to further change … to eliminate terrorism from the networks.”

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She said she hoped it would lead to a “more human internet that cannot be used by terrorists for their hateful purposes”.

Macron said things were moving in the right direction and the presence of the Canadian prime minister, Justin Trudeau, and his “personal engagement” was encouraging.

“They said they support the objectives they will do all to cooperation, they haven’t formally signed up to the Christchurch Call but we will do all we can to have a more concrete and formal engagement. The fact the US administration has said it shares our objectives is a positive element,” Macron said.

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.

Ardern said Facebook had made a changes to its livestreaming, announced at the same time as the summit, under which the Christchurch terrorist “would not have been able to livestream his act of violence”.

She said: “That is just one element of the work of we must do. Ultimately we want to be in a position to prevent harm in the first place, to make sure that lives aren’t lost.”