In a tweet, U.S. President Donald Trump sent "warmest sympathy and best wishes" to the people of New Zealand. What looked like the same weapons appeared in the livestream of the mosque attack on Friday.
In Australia, police in New South Wales said there were increasing patrols around mosques as a precaution. Two other people were being held in custody and police were trying to determine how they might be involved.
A further 48 people were rushed to Christchurch Hospital with gunshot wounds, 20 in a critical condition.
"At this stage, we will not be discussing the offenders' possible motivations or the causes of this incident".
Bangladeshi Minister of State for Foreign Affairs Shahriar Alam said it was "extremely lucky" the country's cricket team, in Christchurch for a match against New Zealand, did not suffer casualties.
"What has happened in Christchurch is an extraordinary act of unprecedented violence".
British tabloids are sharing videos of a violent terror attack in New Zealand, despite police issuing a plea not to.
Shortly afterwards a second shooting began at the Linwood Avenue mosque, on the eastern side of city, where seven more were killed.
Prime Minister Ardern had explained that while many people impacted by the shootings were migrants and refugees, "They have chosen to make New Zealand their home, and it is their home".
The chief executive of Calderdale Council Robin Tuddenham said on Twitter: "Tragic and distressing news from New Zealand". His manifesto was also circulated online.
"We would strongly urge that the link not be shared".
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.
"I can confirm that the individual who was taken into custody... is an Australian-born citizen", Morrison said at a press conference, aired at Periscope.
German Chancellor Angela Merkel said she mourned "with New Zealanders for their fellow citizens who were attacked and murdered out of racist hatred while peacefully praying in their mosques".
A forth person arrested on Friday who was in possession of a firearm, but with the intention of assisting police, has since been released. "But we can not assume there are no others at large", Commissioner Mike Bush told reporters. "I just don't understand it". All Christchurch schools have been shut. Two improvised explosive devices found in one vehicle after the shootings have been defused by police.
"We're also removing any praise or support for the crime and the shooter or shooters as soon as we're aware". "They've been made safe by the defence force", Bush told reporters. One man in his late 20s has been charged with murders.
One of the gunmen - believed to be an Australian extremist - livestreamed the deadly assault, stoking outrage and fear that others may be targeted in copy-cat attacks. "Two are still under investigation", Bush said at a briefing aired by the New Zealand Herald.
"It is clear that this can now only be described as a terrorist attack", said Prime Minister Jacinda Ardern, describing the attacks in the city of Christchurch as "one of New Zealand's darkest days".
At the same time, the Canterbury District Health Board said that at least 48 people, including little children, were being treated at the Christchurch Hospital.