Horrific live footage of the Christchurch mosque shootings, apparently taken by a gunman, was still circulating on Facebook shortly before 5.30pm on Friday, hours after it was posted to social media.

The live video, which appeared to be taken from a camera attached to the gunman, was also uploaded to Youtube a short time after the shooting.

Facebook spokeswoman Antonia Sanda was not immediately able to confirm when Facebook first became aware of the footage but said it had been working with "law enforcement" to remove it.

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"We are working very hard to get all of this off the platform," she said.

Spark spokesman Andrew Pirie said the company, Vodafone and the country's third largest internet provider Vocus had agreed to block their customers accessing three overseas websites that would not be known to most New Zealanders but which had provided access to the video.

Pirie said he believed New Zealand internet providers had never previously taken such a step.

"The circumstances are such that we believe it is the responsible thing for the industry to do," he said.

Spark would not be blocking access to Facebook, he said, saying that would be "an extreme step" and there were other avenues to tackle the issue of footage being reposted to the platform.

A spokeswoman for Google, which owns YouTube, said it removed a video and would work closely with the New Zealand authorities to offer any assistance it could.

"Our hearts go out to the victims of this terrible tragedy.

"Shocking, violent and graphic videos have no place on our platform, and are removed as soon as we become aware of them," she said.

At least 100 people had viewed a version of the video and more than half a dozen people had left comments shortly after it had been uploaded moments following the shooting.

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