Facebook chief Mark Zuckerberg has vowed to "step up" to fix problems at the social media giant, as it fights a snowballing scandal over the hijacking of personal data from millions of its users.

"We have a responsibility to protect your data, and if we can't then we don't deserve to serve you," Zuckerberg said Wednesday in his first public comments on the harvesting of Facebook user data by a British firm linked to President Donald Trump's 2016 campaign.

Zuckerberg announced new steps to rein in the leakage of data to outside developers and third-party apps, while giving users more control over their information through a special toolbar.

"This was a major breach of trust and I'm really sorry that this happened," Zuckerberg said in a televised interview with CNN.

"Our responsibility now is to make sure this doesn't happen again."

Zuckerberg said he will testify before Congress if he is the person at Facebook best placed to answer their questions, and that he is not opposed to regulating internet titans such as the social network.

"I am actually not sure we shouldn't be regulated," the Facebook co-founder and chief told CNN.

"Technology is an increasingly important trend in the world; the question is more the right regulation than should it be regulated."

Zuckerberg said measures had been in place since 2014 to prevent the sort of abuse revealed over the weekend but the social network needed to "step up" to do more.

The scandal erupted when a whistleblower revealed that British data consultant Cambridge Analytica (CA) had created psychological profiles on 50 million Facebook users via a personality prediction app, created by a researcher named Aleksandr Kogan.

The app was downloaded by 270,000 people, but also scooped up their friends' data without consent -- as was possible under Facebook's rules at the time.

Facebook says it discovered last week that CA may not have deleted the data as it certified.

"We should not have trusted Cambridge Analytica's certification, and we are not going to make that mistake again," Zuckerberg said.

Facebook is reviewing how much data was accessed by every app at the social network, and will conduct full forensic audits if it notices anything suspicious, according to its chief executive.

(AFP)