The man who livestreamed himself attacking a Christchurch mosque and murdering at least 49 people identified himself online before the rampage as Australian citizen Brenton Tarrant.

On a now-deleted Twitter account, Tarrant posted multiple photos of what appear to be machine gun magazines and a link to what is being described as a manifesto for his actions, theguardian.com reported.

The 74-page document starts off quoting a Dylan Thomas poem, Do not go gentle into that good night, and then moves onto a rant about white genocide.

Tarrant outlines his motivations: including to ‘create an atmosphere of fear’ and to ‘incite violence’ against Muslims while offering up autobiographical details.

Tarrant, an Australian citizen who is believed to come from the northern New South Wales town of Grafton, entitles his document ‘The Great Replacement’.

In it he claims he had ‘brief contact’ with Norwegian mass-murderer Anders Behring Brevik and that Brevik gave a ‘blessing’ for his attack.

Police have not confirmed that Brenton is one of the men in custody over the shooting. They have said one man has been charged.

Australian prime minister Scott Morrison said an Australian citizen was involved in carrying out the attack.

In the document, Brenton introduces himself as growing up working-class, in a low-income family.

‘I am just a regular white man, from a regular family, who decided to take a stand to ensure a future for my people,’ he writes.

‘My parents are of Scottish, Irish and English stock. I had a regular childhood, without any great issues.’

Tarrant details his lack of interest in his education growing up and how he had barely achieved a passing grade in high school and had not attended university.

‘I worked for a short time before making some money investing in [cryptocurrency] Bitconnect, then used the money from the investment to travel,’ Tarrant writes.

News reports from the Grafton Daily Examiner from 2010 show Tarrant had been a personal trainer at the Big River Squash and Fitness Centre.

In a question-and-answer section of the manifesto, he claims he was not seeking fame and is actually a ‘private and mostly introverted person’.

He describes himself as an ‘ethno-nationalist’ and a ‘fascist’.

Tarrant says the attack had been planned for two years and the Christchurch location was scoped out three months in advance.

His choice of weapon – firearms – was designed to gain maximum publicity.

‘I chose firearms for the affect it would have on social discourse, the extra media coverage they would provide and the affect it could have on the politics of United States and thereby the political situation of the world,’ he writes.

New Zealand was not the original choice for the attack but Tarrant wanted to send a message that ‘that no where in the world was safe’.

‘I only arrived to New Zealand to live temporarily whilst I planned and trained, but I soon found out that New Zealand was as target rich of an environment as anywhere else in the West,’ he writes.

‘Yes. It is a terrorist attack.’