It took place on Yom Kippur, Judaism's holiest day.
It appeared to be conducted in a similar way to the March 15 attack; the gunman filmed the attack via a camera on his helmet, and the 35-minute video was posted to a live-streaming video platform.
He reportedly tried to force his way into the synagogue, where 70 to 80 people were, but was unable to.
Two people have been killed, and one person has been arrested.
Amazon had signed up to the Christchurch Call two weeks ago, joining more than 50 countries and organisations, as well as seven other online platforms.
The call includes a crisis-response framework for tech companies and countries to work collaboratively to stop the spread of terrorist or violent extremist content online.
Prime Minister Jacinda Ardern said the framework was implemented immediately.
Tech companies have also activated their own systems to be on alert for the content.
Christchurch Call countries, relevant internet service providers and NGOs have also been notified to ask for people to share information about where they have seen the video.
READ MORE:
• Christchurch Call counters copycat shooting in Germany - PM
• 2 dead, 1 arrested in 'anti-semitic' shooting near synagogue in Germany
But the Herald understands excerpts of the footage, including the shooting scene, have been posted on Twitter, while comments have directed people to excerpts on YouTube.
It has also been posted on 4Chan along with a lengthy discussion, and it has been torrented by 4chan users in a number of places including liveleaks, bitchute, kiwifarms and deathaddict.
Twitch runs channels that enable gamers to watch each other playing online games, and the larger of these channels have around 15 million subscribers.
Ardern announced the new crisis-response framework in New York and said it was ready for deployment.
Part of the motivation was the lack of an effective protocol at the time of the March 15 terrorist attack in Christchurch.
"Out of here [the Beehive] we were trying to make contact with the likes of YouTube and Facebook and Twitter and Microsoft (LinkedIn) and saying, 'What are we doing?' " Ardern has said of the March 15 response.
The new protocol was partly in anticipation of March 15 copycat attacks.
"Of course after the 15th of March in Christchurch, we were very aware that there was every chance that that kind of streaming of such a horrific event could happen again," Ardern told reporters this morning when asked about the attack in Germany.
"The incident protocol we developed has kicked in ... as I understand straight away. Companies are talking to each other to try and stop the [video's] spread."
The protocol includes a shared list of country and company contacts to ensure a swift response.
It has strict actions including sharing of hashes (digital fingerprints to identify content and how to remove it), URLs, and keywords, as well as takedown measures.
Meanwhile the Department of Internal Affairs deemed the footage from Germany to be objectionable content.
The March 15 video footage has also been deemed objectionable, meaning possessing, sharing or downloading it is an offence under New Zealand law.
