He was remanded in custody and is set to reappear in court April 5.
"The police don't have a clue how many guns there really are in New Zealand", said Philip Alpers, an Australia-based expert in gun laws and director of GunPolicy.org.
New Zealand prime minister Jacinda Ardern has said that gun laws will be reformed after the attacks, as legislation allowed the suspect the legally obtain a semi-automatic weapon.
"I have asked our agencies this morning to work swiftly on assessing whether there was any activity on social media or otherwise, that should have triggered a response".
Footage of the attack on one of the mosques was broadcast live on Facebook, and a "manifesto" was also posted online that denounced immigrants as "invaders".
Worshippers, possibly dead or wounded, lay huddled on the floor of the mosque, the video showed. The camera attached to his head recording the massacre follows the barrel of his weapon, like some macabre video game.
Mourners place flowers as they pay their respects at a makeshift memorial near the Masjid Al Noor mosque in Christchurch, New Zealand, Saturday.
According to the Independent, the suspects are alleged to have called people attending Friday prayers at a near-by mosque "terrorists'". No images have emerged from the second mosque.
Tarrant was arrested in a vehicle, which police said was carrying improvised explosive devices, 36 minutes after they were first called.
A Met Police spokesman told Daily Star Online: "It was reported that three males got out of a blue Ford Fiesta and attacked another man with a weapon - believed to be a hammer or other blunt object".
Ms Ardern said she would be reviewing events leading up to the attack to see how the suspect went unnoticed by authorities.
King Salman described the attack as a "heinous massacre" that "underlines the responsibility of the worldwide community to confront the rhetoric of hatred and terrorism".
In total, the mayor's office says there are roughly 800,000 Muslims living in New York City, and about 250 mosques throughout the five boroughs.
"Just around the entrance door there were elderly people sitting there praying and he just started shooting at them", Mazharuddin told Sky.
Police said two other people were in custody.
Gov. Andrew Cuomo directed State Police to increase patrols near houses of worship, saying in a statement, "At a time of great division, we will stand up to hate in all its forms and do everything in our power to protect the safety and well-being of all New Yorkers".
Ardern said 39 people remained in hospital, 11 of them in intensive care. Health officials said 48 other people were being treated at Christchurch Hospital for gunshot wounds. "If they are not of our people, but live in our lands, they must be removed". "Hi guys how are you".
New Zealand's Prime Minister Jacinda Ardern.
Shortly after he told his 51.9 million followers he'd been on the phone with the New Zealand's leader Jacinda Ardern to say he loves the country and that the U.S. stands in solidarity with them and is willing to provide any assistance.