Billionaire investor and liberal political activist George Soros has issued a call for Europe to "please wake up" and recognize "the magnitude of the threat" it faces from what he said were its enemies, both internal and external.

Europe "is sleepwalking into oblivion," the legendary investor warned in an opinion piece published by Project Syndicate on Monday, "and the people of Europe need to wake up before it is too late."

"If they don't, the European Union will go the way of the Soviet Union in 1991," he said, alluding to the dramatic dissolution of the USSR and the fall of Communism in 1991.

The European Union (EU) is experiencing a "revolutionary moment" and the eventual outcome is "highly uncertain," Hungarian-American investor Soros added.

Worse still, Soros believed that neither Europe's leaders nor ordinary citizens appreciated this fact.

The current leadership is reminiscent of the politburo (the principal policy-making committee in the Soviet Union) when the union collapsed, Soros said, "continuing to issue ukazes (orders) as if they were still relevant."

European Parliament elections in May 2019 were the next inflection point for the bloc. Anti-establishment, euroskeptic parties are expected to perform well.

"Unfortunately, anti-European forces will enjoy a competitive advantage in the balloting. There are several reasons for this, including the outdated party system that prevails in most European countries, the practical impossibility of treaty change, and the lack of legal tools for disciplining member states that violate the principles on which the European Union was founded," he said.