European lawmakers demanded answers from Facebook on Tuesday over a major data breach, as Britain's information watchdog sought a warrant to search the London offices of the analysis firm involved.

Facebook has launched its own investigation into claims that data from up to 50 million of its users was harvested by a British company, Cambridge Analytica, and used in US President Donald Trump's election campaign.

But it was forced to suspend the probe late Monday following a request from Britain's information commissioner, Elizabeth Denham, who is making her own inquiries into both companies.

She is seeking court approval to conduct her own searches at Cambridge Analytica, which has strongly denied any wrongdoing.

"We are seeking a warrant so that, as the regulator, we can go in and get to the bottom, search the servers, do a data audit," Denham told BBC radio.

"We are also looking at Facebook at the same time, so our advice to Facebook was to back away, let us get in there as a regulator and do our work, and they have agreed."

A British parliamentary committee called on Facebook founder Mark Zuckerberg to personally explain to them what happened with "this catastrophic failure of process".

But committee chairman Damian Collins said Facebook officials had "consistently understated" the risk of data being taken from users without consent.

Guy Verhofstadt, who leads the European Parliament's liberal group, also called Tuesday for an investigation into what he said was an "absolute scandal".

EU Justice Commissioner Vera Jourova, who has called the breach "horrifying", will meanwhile seek clarification from Facebook during a visit to the United States this week.

US lawmakers have already called on Zuckerberg to appear before Congress, along with the chief executives of Twitter and Google.

They said the firms have "unprecedented amounts of personal data" and the lack of oversight "raises concerns about the integrity of American elections as well as privacy rights".

Amid fears of a regulatory crackdown, Facebook shares fell by 6.8 percent on the Nasdaq index on Monday and were down two percent at $169.17 in early trading on Tuesday.

Safeguards in place

Facebook says the data was taken without its knowledge or consent, and has suspended the accounts of Cambridge Analytica and some of its associates.

It has hired forensics firm Stroz Friedberg to "conduct a comprehensive audit" of the British firm, which it said had agreed to comply and provide access to its servers and systems.

Their experts were at the company's London offices on Monday night when the information commissioner asked them to withdraw.

Although her focus is on Cambridge Analytica, Denham said on Tuesday there are questions about whether Facebook had adequate safeguards in place to protect its users' data.

"There are provisions in the Data Protection Act that require a platform like Facebook to have strong safeguards in place," she said.

"So, we are looking at whether or not there were safeguards, and whether or not Facebook acted appropriately when things went wrong."

Cambridge Analytica has also strongly denied the allegations against it.

A former employee claims it developed an app downloaded by 270,000 people to scoop up information about their friends, which were then used to design software to predict and influence voters' choices at the ballot box.

The company blames the academic who developed the app, University of Cambridge psychologist Aleksandr Kogan, for misusing the data.

It says the data was never used on the Trump campaign, and has anyway been deleted.

Facebook says Kogan violated their rules by passing the data onto a third party, and the app was removed in 2015.

It said he and Cambridge Analytica had confirmed the data had been destroyed, but recently found out this was not the case.

© 2018 AFP