The gunman, who identified himself as Brenton Tarrant from Grafton, NSW, Australia, stormed the Al Noor Mosque in Christchurch on the country's South Island about 1.30pm, opening fire with a semi-automatic shotgun and a rifle on about 100 defenceless worshippers attending Friday prayers.
The leader of CAIR also called out U.S. President Donald Trump, saying he is partially to blame for the terrorist attacks.
An emotional Morrison offered his sympathies to Kiwis.
Google said it's working to remove the footage as soon as possible from YouTube, and it would work closely with authorities to provide assistance. "I fear we all know the answer unfortunately".
Reports of the attack are conflicting, variously presenting the attacks as taking place at one or two mosques in Christchurch.
Syed Ahmed was among those worshipping at a mosque on the New Zealand city's Linwood Avenue on March 15 when he says a man wearing a black motorcycle helmet and camouflage clothing begin shooting from outside.More news: UEFA Champions League Quarter-Final Draw Revealed
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Mr Bush says three men and one woman are in custody.
One man was arrested and charged with murder, and two other armed suspects were taken into custody while police tried to determine what role they played.
Christchurch, a relatively small city in the south of New Zealand, hit global headlines in 2011 when it was struck by a deadly quake.
Ardern asserted in the strongest terms that "it is clear that this can now only be described as a terrorist attack".
The Federation of Islamic Associations of New Zealand (FIANZ) today urged Mulims to "remain calm and display common sense" in the wake of the country's deadliest mass shooting.
The Indonesian Embassy in Wellington sent a team to Christchurch that is coordinating with New Zealand officials. "The persons who has perpetuated this violence against us. have no place in New Zealand". "Many of those affected will be members of our migrant communities New Zealand is their home they are us", Ms Ardern said.
"We need to make sure no-one shares what is online because the risk of copycats is very high, as is the risk of striking out", he said.