The suspects' ideology and preparation for the attack - Prime Minister Ardern described them as having "extremist views", but New Zealand's police commissioner said the man charged with murder was not known to intelligence services.
Mayor of London Sadiq Khan also shared a video on Twitter, recording a message that ended: "When the flames of hatred are fanned, when people are demonised due to their faith, when we play on people's fears rather than addressing them, the consequences are deadly, as we have seen so sadly today".
He added: "I am just a regular White man, from a regular family".
The manifesto said he carried out the attack "to show the invaders that our lands will never be their lands, our homeland are our own and that, as long as a white man still lives, they will NEVER conquer our lands and they will never replace our people".
On the other hand, Foreign Minister Shah Mehmood Qureshi also condemned the terrorist attack in New Zealand in strongest terms.
A number of improvised explosive devices found on vehicles after the shootings were defused by police.
"We're hoping that, over time, people will see sense and understand that violence doesn't create any kind of peace or stability".
Bury St Edmunds MP Jo Churchill Tweeted on Friday morning: "Our condolences to the people of Christchurch New Zealand". Born in Australia to a working class, low income family. I had a regular childhood, without any great issues.
"Police are now in attendance at a property of Somerville Street, Dunedin", the New Zealand force said on Twitter.
In a statement, The General Secretariat of the Council of Senior Scholars said "We call on the whole world, its countries, as well as its organizations and its institutions to criminalize all racist rhetoric", according to Saudi state news agency SPA.
Worshippers, possibly dead or wounded, lay huddled on the floor, the video showed.
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Police stand outside a mosque after the shooting.
"We stand here and condemn absolutely the attack that occurred today by an extremist, right-wing, violent terrorist", Morrison told a press conference.
Afghanistan's Taliban movement - Islamic militants who carry out near-daily attacks on Afghan security forces - also condemned the shooting rampage, calling it an "unforgivable crime".
A Twitter account with the handle @brentontarrant posted on Wednesday images of a rifle and other military gear decorated with names and messages connected to white nationalism.
Six Indonesians had been inside one of the mosques, with three managing to escape and three unaccounted for, its foreign minister said.
Media later reported that not one but two mosques had been attacked.
In full, Her Majesty said: "I have been deeply saddened by the appalling events in Christchurch today".
"We have one person in custody but we are unsure if there are other people". After parking, he took two guns and walked a short distance to the mosque where he opened fire. The video then cuts out.
Australian citizen Brenton Tarrant is believed to be the key suspect in the Christchurch mosque mass shootings.
Traini's lawyer Gianluca Giulianelli said on the radio that his client had repented and "firmly dissociates himself" from the New Zealand killer.