In the video, dozens appeared to be wounded or deceased, with reports circulating that a gunman opened fire at another Christchurch mosque.
Unlike in the United States, where calls for greater gun control after mass shootings are often met by deaf ears when it comes to federal regulation, three mass shootings - only one of which happened in New Zealand - prompted legislative changes.
"This shows that extremism is still flourishing in many places", she said.
"I can tell you one thing right now: our gun laws will change", said Ardern. According to law enforcement officials, the man has been charged with murder and is scheduled to appear in a Christchurch court on Saturday. Seven were killed at the Linwood mosque nearby, and one victim passed away at the hospital.
Prime Minister Jacinda Ardern has described this as one of the country's "darkest days", while around the world political and religious leaders have expressed their condemnation of the attack. As New Zealand has stood by us so we stand shoulder to shoulder with them, and with Muslims in New Zealand, here in the United Kingdom and around the world.
The man in the shocking video described himself as Brenton Tarrant, a 28-year-old Australian. "Many of those affected will be members of our migrant communities - New Zealand is their home - they are us".
Swedish YouTuber Felix Kjellberg, AKA PewDiePie, has said he is "absolutely sickened" to have been mentioned by the suspect in the New Zealand mosque shootings during a livestream of the attacks. In the manifesto, he said white people are failing to reproduce and are being replaced by the "non-European population" as a result of mass immigration - something that he called an "invasion".