The mosque shootings in Christchurch which have left at least 49 people dead were a “very well-planned” attack, New Zealand’s police commissioner has said.

Up to 41 people died at one mosque in the South Island city, seven at another and one person died in hospital, Mike Bush told reporters, while more than 30 others have been taken to hospital with serious injuries.

A man in his late 20s, believed to be called Brenton Tarrant, has been charged with murder and is set to appear in court on Saturday, while officers are trying to determine if three other suspects were involved in the attacks.

Asked how long he believed the gunman had been preparing for the attack, Commisioner Bush said: “I couldn’t tell you, but I think - I don’t need to tell you, this is a very well-planned event."

He added two suspected improvised explosive devices were found on one of the suspects' vehicles.

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Video circulated on social media, apparently taken by the gunman and posted online as the attack unfolded, showed him driving to one mosque, entering it and shooting randomly at people inside.

The attacker is also believed to have published a manifesto outlining his intentions, in which he espoused anti-immigrant and Islamophobic ideology.

The Independent, which could not verify its source, has chosen not to publish details of the rambling 74-page manifesto, which cited media exposure as one of his reasons for carrying out the attack and producing the document.

“We’ve seen from one of the offenders that they have publicised their ideology – I’ve no reason to assume anything other than that those others that have been arrested would subscribe to the same ideology, which I can only describe as extreme,” New Zealand prime minister Jacinda Ardern said in a press conference.

She added the presence of suspected explosives "gives us an indication there was a degree of planning around what has happened today".

New Zealand police commissioner says 'one male in his late twenties has been charged with murder'

New Zealand police said the attack had been designated a terrorism and described it as an “unprecedented event” for the country.

“We are unable at this stage to provide details about matters leading up to the attacks. It is very early days and these matters will form part of the investigation,” the force said in a statement.