At his annual dinner at the World Economic Forum in Davos, Mr Soros warned that social media platforms were "obstacles to innovation".

He raised concerns about their power to shape people's attentions.

However, he predicted their days were numbered because tax policy and regulation would catch up with them.

Mr Soros also called the Trump administration a "danger to the world", adding that he believed the president would be gone by 2020 "or sooner".

'Lost freedom'
But the outspoken financier reserved his strongest criticism for what he called the "unprecedented and transformative" effects of large internet firms.

"The power to shape people's attention is increasingly concentrated in the hands of a few companies," Mr Soros told assembled guests.

Referencing Google and Facebook several times during his speech, he said: "It takes a real effort to assert and defend what John Stuart Mill called 'the freedom of mind'.

"There is a possibility that once lost, people who grow up in the digital age will have difficulty in regaining it."

He cautioned that this would have "far-reaching political consequences", and had already played a large role in the election of Donald Trump.

Facebook declined to comment, while Google did not immediately return a request for comment.

The 87-year-old repeatedly praised EU competition commissioner Margrethe Vestager, whom he said would be the social media companies' "nemesis".

Ms Vestager has become best known for going after US tech giants, slapping charges on Google, Amazon and Apple.

Mr Soros said the EU, which has no internet giants of its own, was best placed to "protect society against them", whereas US regulators, he maintained, were too weak.

"Internet monopolies have neither the will nor the inclination to protect society against the consequences of their actions," he emphasised.

'Societies in crisis'
The Hungary-born hedge fund manager, who initially became famous for having made $1bn by betting on the devaluation of the pound in 1992, heads several foundations devoted to "defending open societies from their enemies".

Mr Soros, a Holocaust survivor, opened his speech by disclosing that he found the current moment in history "rather painful".

"Open societies are in crisis, and various forms of dictatorships and mafia states, exemplified by Putin's Russia, are on the rise."

But he predicted that Donald Trump, whom he previously branded a "would-be dictator," might not last to the end of his term.

"I expect a Democratic landslide in 2018," Mr Soros asserted.