"I can tell you one thing right now, our gun laws will change".
Police later said one of the arrests didn't relate to the shootings. "The horrific active shooter scenario at a mosque is something we all pray never happens (but) there is no active intelligence that there is any immediate threat in the U.S. But we can not be complacent".
Police said 41 people died at the Deans Avenue mosque and seven died at the Linwood Avenue mosque.
Ardern said she had asked authorities to look into whether there was any activity on social media or elsewhere ahead of the attack that should have alerted them.
The survivors included 17 members of Bangladesh's cricket team, whose game against New Zealand on Saturday has been postponed, and a Palestinian man who fled for his life after seeing someone being shot in the head.
A vigil was held at Nathan Phillips Square to honour the victims of two mass shootings at New Zealand mosques.
New Zealand's Prime Minister Jacinda Ardern called the shooting a "terrorist attack" and one of the country's darkest days.
Conservative Leader Andrew Scheer has issued a revised statement on the terrorist attacks in New Zealand after being criticized for not mentioning that the attack was against Muslims at mosques during their Friday prayers. Shortly before the attack, he published a 73-page "manifesto" in which he vowed "revenge" against Muslim "invaders" and said he was inspired by Anders Breivik, who killed 77 people in Norway in 2011.
"We are a society, we are a province that has accepted 108,000 people from, I think, over 150 countries all around the world in the last decade".
A man who could not find out information about what happened to his father and two brothers pushed through police barricades at one of the cordons in an effort to get closer.
That Act created a regulation so that anyone over the age of 16, who is a "fit and proper person" and the law defines as "a person of good character who will abide by the Laws of New Zealand", can be legally granted a gun license; which is require in order to buy or own a gun.
The New Zealand prime minister went on to say she had instructed the government bodies to 'report to Cabinet on Monday on these events with a view to strengthening our systems on a range of fronts including, but not limited to, firearms, border controls, enhanced information-sharing with Australia, and any practice reinforcement of our watch list processes'. Friday is Islam's holy day.
Police Commissioner Mike Bush declined to comment on whether it was an act of terrorism but said the situation was unprecedented in New Zealand.
One witness told news website Stuff he was praying when he heard shooting - and then saw his wife lying dead on the footpath outside when he fled.
"There were bodies all over", he said.
The Los Angeles Police Department posted to Twitter that while it had no indication that any related attacks would be carried out in the city, it would increase patrolling around L.A. mosques "out of an abundance of caution".