Sky has removed its Sky News broadcast to avoid the spread of footage of a terror attack at two mosques in Christchurch.

A gunman involved in the shootings, which left at least 49 people dead, livestreamed the attack in a chilling 17 minute video.

A spokeswoman for SKY TV NZ said the decision to remove the news channel from the platform was made in light of yesterday's tragic events.

"We made the decision to remove Sky News Australia from our platform while disturbing footage of the shootings was being shown to avoid causing any distress to our viewers," she said.

"It will remain off air until we are confident the footage won't be shared."

The broadcast had been replaced with Fox Sports.

The change applied to the New Zealand broadcast of Sky News - including on the online platform Sky Go.

Sky News was still being broadcast in Australia, as Sky Australia was a separate company.

The video referenced was a live stream, accessible through posts on at least two social media platforms yesterday afternoon.

Using what appeared to be a helmet-mounted camera, the gunman livestreamed in horrifying detail 17 minutes of the attack on worshippers at the Al Noor Mosque, where at least 41 people died.

Several more worshippers were killed at a second mosque a short time later.

The video was widely available on social media for hours after the horrific attack.

Facebook said it took down a livestream of the shootings and removed the shooter's Facebook and Instagram accounts after being alerted by police.

Twitter and YouTube owner Google also said they were working to remove the footage from their sites.

The furor highlights once again the speed at which graphic and disturbing content from a tragedy can spread around the world and how Silicon Valley tech giants are still grappling with how to prevent that from happening.

Meanwhile, Facebook users are using the platform to show their solidarity with those affected by the attack.

People were updating their profile photos with 'frames' - which added messages like "New Zealand is their home - They are us" to the image.

Another frame said "This is not who we are! Kia Kaha Christchurch".

Prime Minister Jacinda Ardern this morning reminded the public not to watch, nor share video circulating of the attack.

"There are penalties that apply to the distribution of objectionable material," she said.

She called the footage "extremely disturbing" and said authorities were doing what they could to remove it.