Billionaire investor and liberal political activist George Soros launched a blistering attack on Chinese President Xi Jinping on Thursday, describing him as the "most dangerous" opponent to those who believe in open society.

Speaking at the World Economic Forum during a private dinner event in Davos, Switzerland, Soros lambasted Xi's proposed social credit rating system.

His comments come as the Chinese state continues to set up a broad ranking system to monitor its citizens, giving them a social credit score.

"I want to call attention to the mortal danger facing open societies from the instruments of control that machine learning and artificial intelligence can put in the hands of repressive regimes," Soros said.

"The social credit system is not yet fully operational, but it's clear where it's heading. It will subordinate the fate of the individual to the interests of the one-party state in ways unprecedented in history."

First announced in 2014, the government-run system will track elements of individual people's behavior and determine some personal privileges for them based on a score.

China is piloting the system in various locations, and it is not clear how it will work after it fully rolls out nationally. So, for example, if a person were to get a traffic violation or criticize the government, their personal score may decline. People with lower scores may face penalties, such as being banned from traveling on certain train lines or getting their children into prestigious schools.

The system, which is due to be fully operational in 2020, is expected to be mandatory.

The head of Soros Fund Management and the Open Society Foundations said the system was "frightening" and "abhorrent."