Another person died at the hospital. "I am calling on the world, in particular the West, to take quick measures", he said.
"London stands with the people of Christchurch in the face of this horrific terror attack", he said. "For people of all religions and of none, a red line has been crossed", Israeli President Reuven Rivlin wrote on his official Twitter feed.
Norwegian Prime Minister Erna Solberg said the attack sparked memories of the 2011 massacre of 77 people by extremist Anders Breivik at a left-wing youth gathering on a Norwegian island and with a bomb in Oslo.
"It's obviously very sad".
The third cricket test was cancelled, New Zealand Cricket said later.
Members of the Bangladesh cricket team, now on tour in New Zealand, said they had almost been caught up in the tragedy.
Italy's far-right Interior Minister Matteo Salvini voiced his "absolute condemnation" of the New Zealand killings, in a statement.
The Gulf countries followed suit and offered their condolences to the families of those affected by the attack.
Britain's Queen Elizabeth said she was "deeply saddened by the appalling events in Christchurch today". "We should pray for the people of New Zealand, but especially communities around Christchurch that have suffered so much in recent years".
A police presence has been placed at mosques around the country and ramped up throughout Christchurch.
"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.
The police described the move as a precaution as "there is no ongoing or specific threat to any mosque or place of worship" in the state.
British boyband Blue wrote: "Last month we had the honour of playing our first show in New Zealand in over 15 years and can attest to the warm generous nature of New Zealanders".
In a video posted to YouTube, she said: "Through terror attacks that have taken place on United Kingdom soil we know only too well the pain that such horrifying attacks can cause".
Political and religious leaders around the world expressed disgust and sorrow at the deadly shooting at two mosques in New Zealand on Friday, with some blaming politicians and the media for having stoked hatred of Muslims that led to the attack.
"Japan is determined to resolutely stand up against terrorism".
Prime Minister Ardern previously described the attack as "one of New Zealand's darkest days", adding: "What has happened here is an extraordinary and unprecedented act of violence".
Police commissioner Mike Bush urged people to stay away from mosques and told those living in Christchurch "close your doors until you hear from us again".
"Harrowing news from New Zealand overnight" said EU Council president Donald Tusk.
Two of the others remain in police custody, with a fourth person arrested deemed not to have been involved in the attacks.
Ms Ardern said: "Many directly affected by this shooting may be migrants to New Zealand; they may even be refugees here".
"We are a proud nation of more than 200 ethnicities, 160 languages".
Speaking at the funeral of a former minister, Erdogan said the anti-Islam hatred that motivated the attacks "has rapidly started to take over Western communities like a cancer".