Prime Minister Jacinda Ardern says the Christchurch Call summit in Paris is about blocking violently horrific content from being uploaded to social media sites, as well as stopping it going viral.

And though the summit will not result in globally enforceable rules, she says it will be valuable if the likes of Facebook commit to a preventative approach, rather than continuing to respond long after the damage is done.

"Government responses are reactive. They are all around take-down, whether you have an hour or 24 hours," Ardern told the Herald in an interview before flying to Paris last night.