Some New Zealand businesses have reportedly called a halt to social media advertising in the wake of the Christchurch mosque attacks.

The country’s lottery agency, Lotto, and banks Westpac and TSB had removed social media ads, while other New Zealand businesses were being asked to consider where they spent their money, news website Stuff reported on Tuesday.

Last Friday’s horrific attacks, which left 50 dead and 50 injured, were live-streamed on social media. Facebook has said it took down 1.5 million copies of the footage, while authorities were left scrambling to stop its spread across the internet on Twitter, Google and elsewhere.

Facebook and Alphabet Inc’s YouTube have said they are also using automated tools to identify and remove violent content.

However, New Zealand Prime Minister Jacinda Ardern said the “graphic” vision was still available online.

Ms Ardern said on Tuesday she had been in communication with Facebook chief Sheryl Sandberg, and wanted the social media giant to ensure the “horrendous” footage of the attack was unable to be viewed.

“You can’t have something so graphic and it not [have an impact] … and that’s why it’s so important it’s removed,” she said.

Australian Prime Minister Scott Morrison said on Tuesday he had written to G20 2019 president, Japanese Prime Minister Shinzo Abe, to ark the organisation to consider practical ways to force social media giants such as Facebook and Google to stop broadcasting atrocities and violent crimes.

“These social media companies have built this technology. They’ve created these capabilities,” Mr Morrison said.

“If you 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 these social media platforms.”

Mr Morrison said the global community needed to ensure tech companies met their moral obligation to serve communities they profited from.

“The G20 has worked together to make sure these big companies pay their taxes,” he said.

“I’m sure we can work together to make sure they protect our citizens by ensuring that their tools that they have developed are not used by terrorists as weapons to advance their agendas of hate.”

Senior Labor frontbencher Penny Wong said the companies had demonstrably failed their responsibilities. Changes to laws should be considered if required, she said.

Social media expert Damien Spry, who lectures at the University of South Australia, said Facebook had struggled to cope with the popularity of its live broadcasts.

“Once it is uploaded then it’s almost impossible to take it down before it at least gets spread to a few other users,” he told ABC Radio National.

Greens leader Richard Di Natale said debate about social media should not be used to absolve politicians and mainstream media from their responsibility in fuelling hate speech.

Mr Morrison has also said Australian authorities were watching for the rising threat of far-right extremists following the attacks.

-with AAP