The Chief Censor has classified the Christchurch gunman's "crude booklet" as objectionable.
That means it's now an offence to possess or distribute it.
"It promotes, encourages and justifies acts of murder and terrorist violence against identified groups of people," David Shanks said on Saturday, in justifying the ban.
"It identifies specific places for potential attack in New Zealand, and refers to the means by which other types of attack may be carried out. It contains justifications for acts of tremendous cruelty, such as the deliberate killing of children."
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The document was published online and sent to various people - including the Prime Minister - just minutes before a gunman attacked two mosques in Christchurch, killing 50 people.
"People who have downloaded this document, or printed it, should destroy any copies," Shanks said.
"There is an important distinction to be made between 'hate speech', which may be rejected by many right-thinking people but which is legal to express, and this type of publication, which is deliberately constructed to inspire further murder and terrorism. It crosses the line."
Mr Shanks while most Kiwis would "simply find it repellent", a "small group… may be receptive to its hateful, racist and violent ideology, and… may be inspired to follow the example set by its apparent author".
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Media would not be stopped from quoting the document, but "ethical considerations" should be taken into account.
"We also appreciate that there will be a range of people, including reporters, researchers and academics, who will be in possession of the publication for a range of legitimate purposes, including education, analysis and in-depth reporting. Those individuals can apply for exemptions, so they can legitimately access and hold a copy."
If you find a copy of the "crude booklet" online, Mr Shanks says it should be reported immediately to the site hosting the material, such as Twitter, Facebook, Instagram or YouTube, and you should alert the Department of Internal Affairs.