The leaders of seven countries, including UK's Theresa May and Canada's Justin Trudeau, and representatives from Facebook, Google, Microsoft and Twitter will all be in Paris next week for the Christchurch Call summit.

But US President Donald Trump will not be there, and it is unclear if there will be a US representative at all.

Nor are Facebook boss Mark Zuckerberg or second-in-charge Sheryl Sandberg attending, both of whom Prime Minister Jacinda Ardern spoke with after the March 15 terror attacks.

Instead Nick Clegg, former UK Deputy Prime Minister and Facebook's vice president of global policy & communications, will attend.

Ardern, who is flying to Paris this evening to co-chair the summit with French president Emmanuel Macron, released the names of confirmed attendees this morning.

She did not see it as a snub that Trump, Zuckerberg, and Sandberg were not coming, and said that the attendees were still being finalised and a US representative might still attend.

"Engagement within such a short timeframe is a big ask. We're really pleased with the turnout," Ardern told the Herald.

"We will continue to seek support from others. This is a start. We will then continue engagement and seek additional signatories to the call."

The summit will seek an agreement with countries and tech companies to prevent terrorist of violent extremism content from being hosted on social media platforms.

A broad buy-in for the summit is considered crucial to give it any weight.

The list of attendees includes:

• European Commission President Jean-Claude Junker
• French President Emmanuel Macron
• Canada Prime Minister Justin Trudeau
• UK Prime Minister Theresa May
• Irish Prime Minister (Taoiseach) Leo Varadkar
• Norway Prime Minister Erna Solberg
• Jordan King Abdullah II bin Al-Hussein
• Senegal President Macky Sall
• Indonesia Vice President Jusuf Kalla

Tech companies representatives:

• Twitter chief executive Jack Dorsey
• Microsoft president Brad Smith
• Facebook's Nick Clegg, VP of global policy and communications
• Google's Kent Walker, Senior Vice President for Global Affairs and Chief Legal Officer
• Wikimedia board of trustees member and co-founder Jimmy Wales
• Qwant Co-founder and chief executive Eric Leandri
• NZ Civil Society Rapporteur
• Salwa Toko, the French President Conseil National du Numerique

It is understood that Apple, whose chief executive Tim Cook has been talking to Ardern, supports the summit but feels that it already has successful preventative measures and doesn't want to be perceived as needing to do things differently.

Australian Prime Minister Scott Morrison, who had many phone calls with Ardern following the March 15 terrorist attack, was likely to have attended if it hadn't been the last week before the Australian federal election.

German Chancellor Angela Merkel is also understood to have wanted to be in Paris, but it did not align with her busy schedule.

Ardern has spoken with many of the leaders coming to the summit in the aftermath of the attack, including May, Trudeau and Macron.

She also had a phone call with Trump the day after the attack, and told media afterwards that her message to him was "sympathy and love for all Muslim communities".

For the summit, Ardern said she had tried to reach out to countries that had a similar view on the need for free, open, accessible internet.

But she was open to any country - including those with heavy internet traffic such as China, Brazil and India - signing on to the Christchurch Call after the summit.

Ardern has three key events in Paris: a Voices For Action meeting with civil society members, a round-table meeting with the tech companies, and the Christchurch Call summit with heads of state and the tech companies.

The civil society meeting, which is engagement with key stakeholders in the tech community, will be chaired by Internet NZ chief executive Jordan Carter, who said it would have been good for Zuckerberg to attend.

"In the end, he does make a lot of calls in that company. He's got some very capable senior other people who would add to the useful discussion, but I think it would be great if he did come along."

One of the main issues around what comes from Paris will be whether it will make any difference or even be enforceable. Leaving social media companies to regulate themselveshas not endeared them to many, and did not prevent March 15.

Zuckerberg has called for regulation to set out what should be banned from social media, and require companies to build systems to minimise harmful content.

But Carter said it was important not to set expectations too high, and while he hasn't seen the draft text of the call, he was not expecting a proposal for a global regulatory framework.

"There are no global examples of that for things that happen on the internet. There's no global media law framework. Even if you could get that kind of agreement, it would take a really, really long time."

He said the narrow scope focusing on violent extremism and terrorist content would help get it across the line - with New Zealand leading the charge.

"Presuming they [countries and tech companies] say 'yes', the question will be how you go about doing that."