The video shows the man live-streaming himself as he gets ready to go to the places of worship where the attacks took place and opening fire on those who had gathered for prayers on Friday.
More than 40 people were killed in the attack.
One man, with blood still on his shirt, said in a television interview that he hid under a bench and prayed that the gunman would run out of bullets.
“I was just praying to God and hoping our God, please, let this guy stop,” Mahmood Nazeer told TVNZ.
“The firing went on and on. One person with us had a bullet in her arm. When the firing stopped, I looked over the fence. There was one guy, changing his gun.”
The video then shows the gunman driving off at high speed and firing from his car.
Another video, taken by someone else, shows police apprehending a gunman on a pavement.
Police said improvised explosive devices were found. The gunman’s video had shown red petrol canisters in the back of his car, along with weapons.
The Bangladesh cricket team is in Christchurch to play New Zealand in a third cricket Test, starting on Saturday.
“They were on the bus, which was just pulling up to the mosque when the shooting begun,” Mario Villavarayen, a team coach, told Reuters in a message. “They are shaken but good.”
The Test was cancelled, New Zealand Cricket said later.
Violent crime is rare in New Zealand and police do not usually carry guns.
Before Friday, New Zealand’s worst mass shooting was in 1990, when a gun-mad loner killed 13 men, women and children in a 24-hour rampage in the tiny seaside village of Aramoana.
He was killed by police.
(Additional reporting by Tom Westbrook, John Mair and Swati Pandey in Sydney Writing by Micheal Perry Editing by Robert Birsel and Nick Macfie)