The Chief Censor admits they have got to get a grip on the way documents like the Christchurch gunman's manifesto spread.

Over the weekend the Office of Film and Literature Classification deemed the manifesto objectionable - meaning it's illegal for anyone share or have a copy of it.

The document has been widely available online - and while Chief Censor, David Shanks, told Mike Hosking their rules have been effective, the internet changes that.

"We are in a new environment here and everyone recognises that we are connected to a huge, global network that is sometimes used to propagate these hateful and sometimes dangerous messages."

He said once they looked through the content of the document, they had no choice but to ban it.

"When I first had a look at this document, I was reluctant to give it the profile that making it objectionable could give it, but as we worked it through, according to the framework that we apply to terrorist promotional material, it became obvious to all of us at the office that this was in that category."

Shanks said the consequences for breaking the ban can be severe.

"If you're republishing it, if you're promoting it, if you're using it to extort others to commit acts of violence, then you are subject to some very severe penalties under the law," he said.

However, he said there are exemptions for education or research purposes.

"We are going to be wiring through a process for researchers, academics and journalists."

Preventing the spread of this document is incredibly important, he said.

"This is a horrendous situation in terms of children, in particular, seeing this footage, I can't imagine the ongoing harm that would cause."

"What we are doing now is everything we can to prevent that."