U.S. President Donald Trump is expressing "warmest sympathy and best wishes" to the people of New Zealand after "the terrible massacre in the Mosques".
At least 49 people were killed and 50 others were injured during the rampage.
The first reports of multiple gunshots in Christchurch, the largest city on New Zealand's South Island, came in around 1:40pm local time.
New Zealand Prime Minister Jacinda Ardern condemned the shooting, calling it an "extraordinary and unprecedented act of violence", and adding "this is one of New Zealand's darkest days".
A man has been charged with murder and will appear in court on Saturday morning. Additionally, explosive devices have been defused by police services.
Ardern said many of those in the mosques were likely to be migrants - but "they are us".
Pakistan's Prime Minister Imran Khan echoed those sentiments.
White House press secretary Sarah Sanders described the attack as a "vicious act of hate".
In a message to the Governor-General of New Zealand, the Queen said: "I have been deeply saddened by the appalling events in Christchurch today".
He also gave assurance to stand by the people and the government of New Zealand at this tragic hour.
European Commission President Jean-Claude Juncker tweeted that he learned of the attack "with horror and profound sadness".
"My thoughts are with the family of Afghan origin who was shot and killed in this heinous incident", he wrote.
Forty-one people were killed at the Al Noor mosque, seven at a mosque in the Linwood neighbourhood and one died in hospital, police said.
In a 74-page document posted on Twitter just before the attack, the Christchurch shooter said he "took true inspiration from Knight Justiciar Breivik", using terminology reminiscent of that used by the Norwegian extremist. "London will always celebrate the diversity that some seek to destroy".
He went on to say Canadians join New Zealanders and Muslim communities around the world in grieving. He said he wants the city's Muslims to know that New Yorkers "truly embrace" them and "have their backs".
Turkey´s foreign minister said two Turks suffered non-life threatening injuries in the attack.
Another said he saw his wife lying dead outside as he escaped, with one more saying he witnessed children being shot.
Police and ambulance staff help a wounded man from outside a mosque in central Christchurch, New Zealand on Friday.
The independent Queensland senator also tweeted: "Does anyone still dispute the link between Muslim immigration and violence?".
Both attackers share "this narcissism, this grandiose image of themselves", Swedish terrorism researcher Magnus Ranstorp told AFP.
The scale of the tragedy and the task still ahead became clear as supporters arrived from across the country to help with the burial rituals in Christchurch and authorities sent in backhoes to dig new graves in a Muslim burial area that was newly fenced off and blocked from view with white netting.
"The people we serve, in every neighborhood, must always be free from fear and have the immutable right to worship and live in peace".
Suspect in Christchurch mosque shootings to appear in court
A short distance away, 39 people were being treated in hospital for gunshot wounds and other injuries inflicted in the massacre. A total of 49 people were killed and at least 48 were wounded in two shootings at a pair of mosques in Christchurch .
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