Forty people have been killed and more than 20 seriously wounded in shootings at two mosques in Christchurch.
New Zealand’s Prime Minister Jacinda Ardern described the incidents as a terrorist attack, and one of the country’s “darkest days”.
Three men and one woman are in custody, police commissioner Mike Bush said, but warned more suspects may be at large.
Australia’s Prime Minister Scott Morrison said one of those arrested was an Australian citizen.
He described the suspected attacker as an “extremist right-wing violent terrorist”.
Authorities have advised all mosques in the city to shut down until further notice, saying this was an unprecedented act of violence.
Armed police have also been seen at Papanui High School in Christchurch, which has been cordoned off.
It is not yet known how many shooters there were, but one gunman is an Australian who is believed to have written a manifesto outlining his intentions. In it, he espouses far right and anti-immigrant ideology.
Footage taken by one shooter has emerged, which he appears to have live-streamed as he shot victims in a mosque. Police called on the public not to share the “extremely distressing” material online.
Facebook said it had removed the shooter’s Facebook and Instagram accounts as well as any support voiced for that crime.
The sequence of events remains unclear and has mostly come via eyewitness reports to local media.
