She said her office was one of about 30 recipients and had forwarded the email to Parliamentary security within a couple of minutes of receiving it.
Jacinda added that the terrorist was brought down within 36 minutes of the attack.
In emotional scenes, Ardern earlier met mourning members of the Muslim community in Wellington.
Syrian refugee Khaled Mustafa, who had arrived in New Zealand with his family just months ago, was amongst those killed on Friday.
The death toll of the Christchurch terror attacks has risen to 50, and two injured victims remained in critical condition, Police Commissioner Mike Bush said Sunday morning.
Mohammad Imran Khan, a 47-year-old man who owned two restaurants in Christchurch died in the Lynwood mosque.
New Zealand's Minister for Pacific Peoples Aupito William Sio said he spoke to one of the Trustees of the Festival last night about the decision, and why it was made.
The first victim identified was Daoud Nabi, a 71-year-old grandfather who died trying to save someone else from a bullet, according to his son.
Many victims still missing or injured, families and relatives continue to wait around the hospitals in Christchurch to hear about the fate of their loved ones.
"We struggling with it as much as everyone else".
"We do see gunshot wounds".
Following the horrendous massacre, a 28-year-old Australian man, Brenton Tarrant, has been charged with murder.
New Zealand Massacre suspect was gun club member
NZ Prime Minister Jacinda Ardern says despite the attacks being carried out in Christchurch, he had been based in Dunedin. Handcuffed, shoeless Tarrant appeared in a Christchurch District Court on Saturday and was charged with murder .
Australian Man Appears In Court On Murder Charge After Christchurch Attack
At a roadblock outside the Al Noor mosque on Sunday, about 40 people were standing in silence near scores of bunches of flowers. The Fijian rugby team also expressed their solidarity with the people of New Zealand after the attacks.
NRL: New Zealand Warriors offer free entry after Christchurch mosque attacks
The New Zealand national anthem will also be played. "Given it's game day, there's a limited number of tickets still available", George added.
The suspect was remanded in custody without plea to the High Court in Christchurch on April 5.
Footage of the attack on one of the mosques was broadcast live on Facebook, and a "manifesto" denouncing immigrants as "invaders" was also posted online.
However, because none of the bodies have been returned to the victims' families because of the investigation, many having been unable to bury their dead within the 24 hours customary in Islam.
"We have to be absolutely clear on cause of death and confirm their identity before that can happen", he said. But Bush said police are aware of the Muslim faith's requirement for a prompt burial.
Morrison said that social media companies had "co-operated" since the attack.
Meanwhile, outside the court, major roads in the city center are cordoned off with heavy armed police officers on duty.
"They put themselves in harm's way to stop any further attack - and I do believe they did prevent further attacks".
Church services for victims of the attack were held around the country, including at Christchurch's "Cardboard Cathedral", a temporary structure built after much of the central city was destroyed in a 2011 quake.
Victims came from across the Muslim world, including Indonesia, Malaysia, Turkey, Afghanistan and Bangladesh.
Anyone over 16 can apply for a New Zealand firearms licence, valid for 10 years after completing a safety course and a police background check. He used five guns in the attacks and had a gun license allowing him to legally purchase all of his weapons. Police are still working to identify what type of weapon was used, but Bush said "it's quite obvious" he modified his firearm.
None of those arrested had previous criminal records.
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