An international algorithm expert has warned politicians are at risk of oversimplifying the debate about regulating social media content and risk "collateral censorship" in the process.

Key points: The Christchurch attack was live streamed on Facebook and shared widely

The Christchurch attack was live streamed on Facebook and shared widely Scott Morrison wants world leaders to discuss how to prevent the distribution of violent videos

Scott Morrison wants world leaders to discuss how to prevent the distribution of violent videos Greens call for a debate on the need for public ownership of social media companies

Prime Minister Scott Morrison wants a global crackdown on social media companies after the Christchurch attack was live streamed on Facebook before being shared millions of times.

He is not alone in the calls, with Australia's major party leaders all calling for reforms after footage of the attack was broadcast live for 17 minutes before it was removed.

"If they can write an algorithm to make sure that the ads they want you to see can appear on your mobile phone, then I'm quite confident they can write an algorithm to screen out hate content on social media platforms," Mr Morrison said.

But law professor and algorithm expert Frank Pasquale, from the University of Maryland, said politicians had failed to acknowledge the problem with live streaming.

"It is a difficult task to moderate live content," he said.

"It's not as easy as it's being made out to be in terms of directly applying advertising algorithms to get rid of forbidden content or horrific content."

Professor Pasquale said a potential option was delaying live streams, the way broadcasters do when dealing with sensitive material.

The problem with live streaming

Facebook's live streaming capability allows its almost 2 billion users to simply press a button to broadcast whatever is in front of them immediately.

But the problem for social media sites is that unlike regular posts, there is no algorithm sophisticated enough to detect violence — or anything else that is illegal — in live streamed videos.

Thousands of Facebook employees are already tasked with reviewing streamed videos.

But they mainly rely on reporting tools to stop live feeds, which typically draw their attention to inappropriate content after the fact.

The Christchurch massacre was not the first time the live feature was used to broadcast horrific vision.

In 2017, Facebook founder Mark Zuckerberg pledged to add 3,000 more content reviewers to his team, after a Thai man live streamed video of himself killing his baby daughter.

The same year, the sexual assault of a 15-year-old was streamed on Facebook live in Chicago, and none of the people who watched it reported the incident to police.

The real concern is shared content

Professor Pasquale said while live streaming technology presented certain risks, the "real concern" was live content being shared later.

"There is a lot that could be done to stop the reproduction of it which is by far the more harmful aspect," he said.

On Monday, Facebook said it had removed 1.5 million videos of the attack and was working around the clock to pull down more.

But Professor Pasquale said preventing the videos from being uploaded in the first place — rather than pulling them down — needed to be a priority.

He said one option was for social media companies to make sure a human employee reviewed videos, before they were approved for upload.

"That is one possibility. I'm not necessarily endorsing that, but I think … when we have a critical mass of incidents like this it may well be something that governments start requiring," he said.

Mr Morrison said his Government was looking at some "practical proposals in this area right now".

But he stopped short of proposing new laws to govern online content and the organisations that host it.

He has penned a letter to the chair of June's G20 summit in Osaka, Japanese Prime Minister Shinzo Abe, calling for the issue of social media governance to be added to the top of the agenda.

He said it was "unacceptable to treat the internet as an ungoverned space".

But with the G20 summit scheduled for after May's election, there is a possibility a different prime minister might be discussing those proposals with international counterparts.

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Telecommunication companies block sites

Australia's major telecommunication players said they had temporarily blocked domains that have hosted footage showing material related to the Christchurch attack.

Optus, Telstra and Vodafone all confirmed they had acted in line with community expectations.

"We understand this may inconvenience some legitimate users of these sites, but these are extreme circumstances and we feel this is the right thing to do," a Telstra spokesman said.

A Vodafone spokesperson said while there had been discussions at an industry level, its decision to block sites had been determined independently.

"Vodafone Australia believes there is no place on the internet for this horrific, disturbing content," the company said in a statement.

"We have placed temporary blocks on dozens of sites known to be still actively hosting footage of Friday's shootings in Christchurch."

Politicians want companies to act

Australian Greens leader Richard Di Natale said social media had become essential infrastructure and a debate was needed about public ownership of these organisations.

He also said there was a simple short-term solution in hiring more employees.

"These are massive companies whose sole focus has been to make profit over the public good and that's gone on far too long," Senator Di Natale said.

"You just have enough people who can monitor this stuff and make sure it gets taken down quickly."

Labor leader Bill Shorten echoed Mr Morrison's sentiment that the answer lied in programming.

"I do not believe it is beyond the technological capacity for some of the richest, largest, most powerful, cleverest, most sophisticated businesses in the world, not to be able to better monitor the material before they publish it," he said.

"If they don't do that, they need to be accountable."