"What Japan is doing is quite dangerous," Soros told CNBC's Bernie Lo on the sidelines of a conference by the Institute for New Economic Thinking in Hong Kong.
"If what they are doing gets something started, they may not be able to stop," he said, referring to the yen, which has fallen sharply in recent months on expectations of aggressive monetary easing.
"If the yen starts to fall and (Japanese) people don't want to put their money abroad then the yen's fall could become an avalanche," he said.