As for the suspects, Ardern said, "these are people who I would describe as having extremist views that have absolutely no place in New Zealand".
Bush said that police had also defused 'a number of IEDs (explosive devices) attached to vehicles'.
New Zealand's prime minister said that immigrants and refugees "have chosen to make New Zealand their home, and it is their home". Four people have been arrested - three men and one woman - according to reports, and police have recovered firearms from both the Linwood Avenue and Al Noor Mosque shooting scenes.
Halifax MP Holly Lynch also took to Twitter and said: "Horrific news from New Zealand this morning".
Police describe it as an "active shooter" situation.
Of the 40 people taken to Christchurch Hospital, one has since died from their injuries.
In fact, I am sure right now New Zealand would like me to share a message on their behalf too.
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".
In a statement, a spokesperson for Facebook New Zealand, Mia Garlick, said videos that appeared to show the Christchurch shootings were quickly taken down.
The identities of the victims - further nationalities could be among the casualties, with Afghan and Malaysian government confirming nationals injured in the attack.
"Feeling very sick, that person is brainless and a savage", said one Indonesian twitter user who identified himself as Farhan Adhitama.
In Muslim-majority Malaysia, Anwar Ibrahim, the leader of the biggest party in its ruling coalition, said one Malaysian had been wounded in the attack he described as a "black tragedy facing humanity and universal peace". He then replies: "Just a ordinary White man, 28 years old". It is the second most-populous city in New Zealand behind Auckland and Wellington.
In it, he says he was inspired by mass killer Anders Breivik, who killed 77 people in Norway in 2011.
While there was no reason to believe there were any more suspects, the prime minister said the national threat level was raised from low to high.
Police warned Muslims not to visit mosques "anywhere in New Zealand", a country of almost five million where mass shootings are rare. It's also requesting extra police patrols at their mosque in Old Irving Park, their education center in Morton Grove, and their campus in Skokie. "We stand together against such acts of terrorism". And Air New Zealand canceled several flights in and out of Christchurch.
"From what we know, it does appear to have been well planned", she said, adding that in addition to the dead another 20 people were seriously injured.