Ardern said she never anticipated ever having to voice the grief of the nation and had hoped never to.
She spoke directly to the families. "We cannot know your grief but we can walk with you at every stage."
Ardern said the police officers involved in the arrest of the suspect were heroes, but she acknowledged those who lost their lives trying to stop the gunman after he burst in to two mosques and opened fire.
She paid tribute to the first responders who worked and were still working.
"We are proud of your work and incredibly grateful for it."
Ardern said the nation remained on high alert and while there was no specific threat, the country was maintaining its vigilance.
She said there had rightly been questions about how the atrocity had occurred, and anger that it had.
She promised that all those questions would be answered.
It was not good enough to sit back and allow social media platforms to operate. They needed to take responsibility.
National Party leader Simon Bridges said no one could have imagined the terror about to be unleashed.
That 50 worshippers at the two mosques would have their last day of their lives.
"All of us changed forever."
"New Zealand was somewhere where they could find solace in a world full of problems," Bridges said of the immigrants and refugees who died or were injured.
It was not something that happened only to Muslims or Christchurch. It had happened to all New Zealanders, he said.
"Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars," Bridges said, quoting US civil rights leader Martin Luther King.
New Zealand First leader Winston Peters called the perpetrator of the violence a "coward".
An attack on people practising their beliefs was an attack on everyone's beliefs, Peters said.
He said New Zealand was not alone, and he had received many messages of support from Muslim countries.
The gunman's ways "were not our ways".
New Zealand's essential character would not change in the aftermath of the massacre.
Davidson said the ideology that drove the attacks also wanted to harm other communities.
She told the Muslim community: "We did not protect you. We will do better."
"We need to let you know that we hear you, we get it."
Davidson said it was time to understand that words mattered.
Act leader David Seymour extended condolences to the victims, and condemnation to the perpetrator.
He said that all the bad news was in the world section of newspapers, and he wondered how New Zealand could end up in the bad news section of other countries' papers.