New Zealand internet service providers are working together to block any websites with footage of the Christchurch massacre.

Spark, Vodafone, 2degree and Vocus are actively working collectively to ensure the footage is inaccessible to New Zealanders.

The alleged gunman live-streamed on the internet the attack on two Christchurch mosques that killed 50 people.

Prime Minister Jacinda Ardern asked the public on Friday not to share or engage with any video or anything else posted on the internet by the alleged gunman.

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New Zealand Telecommunications Forum chief executive Geoff Thorn said the move for the country's internet service providers to work together was unprecedented.

He said it was a decision the whole industry agreed on.

"The gunman clearly wanted his actions to be seen, but we do not believe that this is desirable and are doing what we can to prevent this from happening as much as possible," Thorn said, referencing the attack being livestreamed on social media.

Thorn said internet providers were sharing knowledge and that a number of websites had been blacklisted and requests to remove the footage had been made.

"There is the risk that some sites that have legitimate content could have been mistakenly blacklisted, but this will be rectified as soon as possible," he said.

"The industry has a history of co-operating and putting competitive behaviour to one side for the benefit of New Zealanders, of which this is another good example."