As Breitbart News previously reported, nearly 50 people were reportedly killed at a mosque in New Zealand by a shooter who appears to have a manifesto that endorses causes from "socialism to white supremacy to environmentalism".
An ashen-faced Ardern said she was unable to confirm the number of fatalities, with events still unfolding.
Ardern also commented on the spread of images and footage related to the incident on social media, asserting "we should not be perpetuating, sharing, giving any oxygen to this act of violence and the message that sat behind it".
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". "It unites us against extremism, hatred and terrorism, which knows no religion".
At least 49 worshippers have been killed in a terrorist attack at two mosques in a New Zealand city on Friday.
9pm: Death toll rises to 49 and Police Commissioner Bush reveals a man in his late 20s has been charged with murder.
A shooter killed dozens of people in a New Zealand mosque and left behind a manifesto that endorsed a variety of causes on both sides of the political aisle.
Three men and a woman were arrested after the massacre, authorities said, adding that none of them were on any terrorism watch, including in Australia.
New Zealand's charitable healthcare organization St John said 20 of its ambulance cars and operational vehicles had been working on the scene of a firearms incident.
He tweeted: "Our hearts go out to the people of New Zealand following the news of this bad act in Christchurch".
"This is one of New Zealand's darkest days", she said.
'Just around the entrance door there were elderly people sitting there praying and he just started shooting at them, ' he told the New Zealand Herald.
The Linwood Avenue mosque is one of two which have subject to a shooting, with another taking place at a mosque on Deans Avenue.
Police are not looking for any named or identified suspects, he says, but adds that it would be "wrong to assume that there is no-one else".
Mr Sayed, who has been living in New Zealand for over 10 years, told Indian broadcaster NDTV that he had witnessed the man "creep up behind the shooter and hold him until his gun dropped".
The attacks targeted the Masjid al Noor mosque, where 41 people died, and a second, smaller mosque in the suburb of Linwood, where seven more died.
Witnesses claim the gunman was wearing a military style jacket and carrying an assault weapon.
The gunman said he was not a member of any organization, acted alone and chose New Zealand to show that even the most remote parts of the world were not free of "mass immigration".