Americans in their 20s and 30s are facing a retirement crisis that could plunge them back into the Great Depression, Blackstone President and Chief Operating Officer Tony James said Wednesday.

"Social Security alone cannot provide enough for these people to retain their standard of living in retirement, and if we don't do something, we're going to have tens of millions of poor people and poverty rates not seen since the Great Depression," he told CNBC's "Squawk Box."