At least 49 people were killed in mass shootings at two mosques full of worshippers attending Friday prayers in an attack broadcast in horrifying, live video by an immigrant-hating white nationalist wielding at least two rifles.
One man was arrested and charged with murder, and two other armed suspects were taken into custody while police tried to determine what role they played.
"It is clear that this can now only be described as a terrorist attack," Prime Minister Jacinda Ardern said, noting that many of the victims could be migrants or refugees.
She pronounced it "one of New Zealand's darkest days."
The attack shocked people across the nation of 5 million people, a country that has relatively loose gun laws but is so peaceful even police officers rarely carry firearms.
The gunman behind at least one of the mosque shootings left a 74-page manifesto that he posted on social media under the name Brenton Tarrant, identifying himself as a 28-year-old Australian and white nationalist who was out to avenge attacks in Europe perpetrated by Muslims.
Using what may have been a helmet camera, he livestreamed to the world in graphic detail his assault on worshippers at Christchurch's Al Noor Mosque, where at least 41 people were killed. An attack on a second mosque in the city not long after killed several more.
Police did not identify those taken into custody and gave no details except to say that none of them had been on any watch list. They did not immediately say whether the same person was responsible for both shootings.
With files from the Associated Press
Colin P. Clarke, expert on terrorism and senior research fellow at The Soufan Center, a non-profit dedicated to research, analysis and strategic dialogue related to global security issues and emerging threats; he's also an adjunct political scientist at the Rand Corporation
Doug Kouns, a former Special Agent and Supervisory Special Agent of the FBI who worked on criminal, counter-terrorism and counter-intelligence investigations during his 22-year tenure at the Bureau; founder of the Indiana-based intelligence firm, Veracity
Salam Al-Marayati, president and co-founder of the Muslim Public Affairs Council, a nonprofit that works to improve public understanding and policies that impact American Muslim based in Los Angeles and DC
Sally Round, reporter at Radio New Zealand who has been following the story
Alice E. Marwick, professor of media & technology studies at the University of North Carolina at Chapel Hill