Tech Against Terrorism director Adam Hadley said smaller platforms and social media services are where extremists moved to after being shut down by giants like Facebook and Twitter.

"It is like small platforms do not exist," he told a committee reviewing Australian laws that force publishers to remove abhorrent violent material as soon as they become aware of it.

"They are the threat ... (but) smaller platforms ... do not appear to be considered.

"So our frustration here is whilst it is right and proper to apply pressure on the larger platforms, it is not acceptable for terrorists and extremists to have any room to re-manoeuvre."

Violent material spotted by internal artificial intelligence systems and taken down proactively amounted to 99.7 per cent of cases for Facebook and 96 per cent for Twitter.

But smaller platforms do not have access to the resources tech giants do.

This means that while a small amount of terrorist and extremist material makes it way onto Facebook and Twitter, some of these smaller apps are made up almost entirely of terrorist or extremist groups.

Mr Hadley said he was aware of platforms where 70 to 90 per cent of users were terrorist affiliates.

The inquiry also heard a lack of a clear definition for the abhorrent violent material publishers are forced to take down also risks limiting whistleblowing posts.

Representatives of Facebook's parent company Meta and Twitter told the inquiry they supported regulation that forced the takedown of violent and extremist material but more clarity was needed.

Hastily taking down content could lead to the shutting down of "counter-speech", such as people condemning violent material and actions, or journalists, politicians and whistleblowers exposing atrocities.

Meta representatives said they were aware of an instance in the past year where a violent video at a mosque in southeast Asia was taken down by the company but turned out to be exposing violence against Muslims.

Public policy vice president Simon Milner said the company erred on the side of caution after initially believing it was footage of the Christchurch mosque attack and questioned whether there was enough time to make the correct decision.

"Does (the law) allow us to have time to think about it? Once we are aware of it we have to remove it immediately and that is a challenge for us if we want to deliberate," he told the committee.

Twitter Australia senior director Kathleen Reen said 73 per cent of the content on Twitter following the Christchurch attack was from verified accounts, most of which were operated by news organisations and journalists.

"One of the really big takeaways is (the need for) a reasonable process for consultation, for review and for appeal," she said.

"There could be contingencies ... around mass takedowns of content which could effectively block Australians having access to newsworthy content or from understanding what is going on."

Neither Twitter and Facebook had received any official takedown notices from Australian law enforcement agencies.

Australian Associated Press