Scrambling to remove live footage

LONDON — Internet companies scrambled Friday to remove graphic video filmed by a gunman in the New Zealand mosque shootings that 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. At least 49 people were killed at two mosques in Christchurch, New Zealand’s third-largest city.

Using what appeared to be a helmetmounted 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 shooter also left a 74-page manifesto that he posted on social media under the name Brenton Tarrant, identifying himself as a 28-year-old Australian and white nationalist who was out to avenge attacks in Europe perpetrated by Muslims.

“Our hearts go out to the victims, their families and the community affected by this horrendous act,” Facebook New Zealand spokeswoman Mia Garlick said in a statement.

Facebook is “removing any praise or support for the crime and the shooter or shooters as soon as we’re aware,” she said. “We will continue working directly with New Zealand Police as their response and investigation continues.”

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.

British tabloid newspapers such as The Daily Mail and The Sun posted screenshots and video snippets on their websites.