Facebook's Mark Zuckerberg snubs another Christchurch Call meeting with Jacinda Ardern

Mark Zuckerberg has snubbed Jacinda Ardern for a second time.

The chief executive of Facebook won't attend a follow-up meeting on the Christchurch Call in New York next week, despite the Christchurch terror attack being livestreamed on his platform.

But the Prime Minister insists it is action that counts, and on Wednesday Facebook announcing a terrorism crackdown. 

The March 15 Christchurch terror attack was what prompted Ardern's Christchurch Call, an action plan that commits government and tech companies to prevent the spread of terrorist and violent extremist content.

The shooting was broadcast across the world on Facebook, and the video is still circulating online today - but the Prime Minister is adamant the Christchurch Call wasn't a failure.

"I just think it proves why it's so important that it exists," she told Newshub.

She said when she first witnessed the video, it only took her a "matter of seconds to realise what it was... it was horrifying, absolutely horrifying".

A follow-up meeting on the Christchurch Call will take place on Monday while the Prime Minister is in New York for the United Nations General Assembly.

But Zuckerberg will not be attending with his second-in-charge Sheryl Sandberg set to fill in.

Zuckerberg also did not attend the first Christchurch Call summit in Paris in May when a group of world leaders and tech company bosses adopted the pledge.

Ardern said Facebook "absolutely have" been engaging with her, despite Zuckerberg not attending the Christchurch Call meetings.

"For me, whether or not you're physically in attendance is not a demonstration of whether or not you're engaged. For me, it's actually what's done," she told Newshub.

And Facebook has done something: announcing a crackdown on extremism.

To better detect terrorist content, Facebook has been using real-life first-person shooter footage to train its artificial intelligence.

It has also made algorithm changes so anyone searching for extremist content that will be redirected to de-radicalisation sites.

Facebook has also expanded the definitions of terrorism. So far 200 white supremacist organisations have been banned.

National leader Simon Bridges has described the Christchurch Call as a "big talkfest" that has "achieved nothing".

Ardern said it's "ultimately up to the opposition what they choose to attack or not attack".

More announcements on practical steps to make good on the Christchurch Call are expected after the meeting in New York, and Newshub understands more countries have joined the Call.

But there is no firm indication whether the glaring omission, the USA, has signed up.

Ardern will have the opportunity to push for that in her one-on-one meeting with US President Donald Trump on Monday.