Facebook has been accused of "going missing" when it comes to fighting hate speech and playing an "unrestricted role" in terrorist attacks, following two mass shootings at mosques in New Zealand on Friday.

The comments come from Australian Prime Minister Scott Morrison and the country's opposition leader Bill Shorten, who have not held back in criticising the role technology companies have played in amplifying extremist views.

Both politicians warn that the internet has given a home to the kind of white supremacist hate speech espoused by the alleged mosque shooter (an Australian national), saying that tech companies must do more to stamp it out.

In a letter to Japanese Prime Minister Shinzo Abe ahead of the upcoming G20 summit in Osaka, Prime Minister Morrison said internet technologies are playing an "unrestricted role" in the spread of extremism, and that world leaders must lay out "clear consequences" not only for those who carry out terrorist attacks, but also "for those who facilitate them." 

The letter was also sent to New Zealand Prime Minister Jacinta Ardern, who has previously said she plans on discussing the issue "directly with Facebook."

But while Morrison did not mention the likes of Facebook, Twitter and YouTube by name, his political opponent, Labor leader Bill Shorten, was more forthright.

"A platform like Facebook goes to potential advertisers and says, 'We know everything about the users of Facebook, we can tell you everything so that you can geo-target and you can market to them,'" Shorten wrote in an op-ed for the Herald-Sun newspaper. "Well, if that's your business model, fair enough; but you can't go missing when it comes to hate speech."

"Social media is a marvellous tool that has the potential to empower us, but too often it resembles a toxic swamp where wrongdoers can hide and where evil is nurtured," he added.

The comments follow a terrorist attack in New Zealand on Friday, when a gunman entered a mosque in central Christchurch and shot worshippers while they prayed, livestreaming the shooting on Facebook. The attack, which also involved a second shooting at another Christchurch mosque, claimed 50 lives. The alleged attacker, Brenton Harrison Tarrant, was an Australian national.

As New Zealand counts the cost of the deadliest mass shooting in New Zealand history, attention has turned to the role the internet and social media played in the attack.

While Facebook and Twitter deleted the alleged attacker's social media accounts within hours of the attack, footage of the shooting spread quickly. The roughly 17-minute live clip was downloaded from Facebook and re-uploaded across the internet on sites such as YouTube, with some users editing out the more graphic content in an attempt to circumvent censors.

Facebook said it deleted 1.5 million versions of the video within the first 24 hours of the attack.

But Prime Minister Morrison is calling for a tougher approach to weeding out extremist content on the internet, saying technology firms have a "moral obligation to protect the communities which they serve and from which they profit."

He added that social media companies, content service providers and gaming platforms all had a part to play to keep communities safe.

"We know that violent extremists use the internet for recruitment, radicalisation and to carry out their evil acts," the Prime Minister's letter reads. "That they will continue to try to use any means their disposal does not mean governments and technology firms should abrogate their responsibilities to keep our communities safe."

Facebook did not respond to a request for comment.

Originally published March 19, 5:32 p.m. PT.

Update, 9:27 p.m.: Adds comments from Australian opposition leader Bill Shorten.