Global markets are facing a crisis and investors need to be very cautious, billionaire investor George Soros has told an economic forum in Sri Lanka.

China is struggling to find a new growth model and its currency devaluation is transferring problems to the rest of the world, Soros said. A return to positive interest rates is a big problem for the developing world, he said.

The current environment is a serious challenge for markets that "reminds me of the crisis we had in 2008," Soros said, referring to the global financial crisis.

"China has a major adjustment problem," Soros said. "I would say it amounts to a crisis."