YouTube says at one point it had to remove one video per second of the Christchurch mosque attack, and says tens of thousands of copies have now been removed.
The attack at the Al Noor Mosque near Hagley Park and at the Linwood Mosque on Friday left 50 people dead.
Brenton Tarrant, 28, was arrested shortly afterwards and and has appeared in court charged with murder.
Live video which was streamed of the attack was downloaded by numerous people, a YouTube spokesperson said, many of whom then attempted to re-publish it on YouTube in the 24 hours after the incident.
The spokesperson said they had since removed tens of thousands of videos and terminated hundreds of accounts created to promote or glorify the shooter.
"The volume of related videos uploaded to YouTube in the 24 hours after the attack was unprecedented both in scale and speed, at times as fast as a new upload every second," they said.
Footage of the attack was automatically rejected, the ability to sort or filter searches by upload date was temporarily suspended, and searches for the event were directed towards authoritative news sources.
"Our teams are continuing to work around the clock to prevent violent and graphic content from spreading, we know there is much more work to do."
New Zealand's Chief Censor has classified the video footage of the event as objectionable, and it is an offence to either possess or distribute it.
People who have a copy of the footage, or share it, run afoul of the Films, Videos and Publications Classification Act, and they could be convicted and face a fine of $10,000 or up to 14 years in jail.
An 18-year-old man has appeared at Christchurch District Court yesterday charged with breaching the Act.
Brenton Tarrant, 28, was arrested and has appeared in court charged with murder.