Citing right-wing United States commentator Candace Owens as an inspiration, Tarrant also claimed he had been in brief contact with Anders Breivik, the far-right extremist who killed 77 people in attacks in Norway in 2011.
Christchurch, sometimes called the Garden City, has been rebuilding since an quake in 2011 killed 185 people and destroyed many downtown buildings.
Both mosques were full of worshippers attending Friday prayers when the shootings occurred. He has not been publicly identified by officials.
New Zealand's Prime Minister Jacinda Ardern called the shooting a "terrorist attack" and one of the country's darkest days. Regardless of whether terrorist attacks are perpetrated by white or Islamist extremists, their narratives must not be enabled through whataboutery. Facebook, Twitter and YouTube all said they had taken steps to remove copies of the videos.
"This individual has travelled around the world with sporadic periods of time spent in New Zealand", Ms Ardern said on Saturday. "We were chosen for the very fact that we are none of these things". "We represent diversity, kindness, compassion, a home for those who share our values, refuge for those who need it. If I don't survive the attack, goodbye, godbless and I will see you all in Valhalla!"
The faithful gathered for prayers on Friday at the Windsor Mosque, a day after a gunman killed 49 people at two mosques in Christchurch, New Zealand.
Huang Yan, the manager of the Christchurch branch of China's Southern Airlines, told Xinhua the mass shooting would bring negative impact on New Zealand tourism as Christchurch has just been recovered from the aftermath of the 2011 deadly natural disaster. He claimed to represent Europeans and whites in a battle against immigrants, people he repeatedly described as "invaders".
The Council on American-Islamic Relations, the nation's largest Muslim civil rights and advocacy organization, condemned the attack.
All mosques across New Zealand have been urged to close their doors for the time being, and in Scotland, police have stepped up patrols around mosques - however, officers insist there is no intelligence to suggest a specific threat in this country.
Service at a mosque in Gibsonia
New Zealand's ambassador-designate to the U.S., Rosemary Banks, told NPR that authorities are "convinced this particular event is over".
"Many of those who will have been directly affected by this shooting may be migrants to New Zealand, they may even be refugees here".
"Israel mourns the wanton murder of innocent worshippers in Christchurch and condemns the brazen act of terror in New Zealand. Our thoughts and prayers are with the victims and their families", White House Press Secretary Sarah Sanders said Friday.
There are about 1.5 million privately owned firearms in New Zealand, according to the most recent from 2017 data by GunPolicy.org, a global database compiled by the University of Sydney.
"Active shooter drills, situational awareness train our ushers and greeters about how to lock down the facility, where our evacuation routes are in the building", Orsini said.
Until yesterday morning, Brenton Tarrant was just another Australian living overseas, travelling when he could, and posting rubbish on social media.
None of those in custody were on any active security watch lists, either in New Zealand or Australia, Bush said.
A 28-year-old Australian man charged with murder appeared in the Christchurch District Court on Saturday morning following Friday's terror attacks on two mosques in the city.
"We are really not feeling safe at the moment", he added.