The rise of China need not be a threat to either Japan or the United States, although Tokyo and Beijing may need some time before they get comfortable with their coexistence as two major powers in Asia, U.S. Ambassador to Japan Thomas Schieffer told a recent symposium in Tokyo.

The U.S. envoy also noted that despite widespread forecasts that China would overtake the U.S. as the world's biggest economy in decades to come, its future prosperity is not guaranteed as the nation faces a host of economic, political and social challenges.

Schieffer was the keynote speaker at the Jan. 23 symposium organized by Keizai Koho Center and the Massachusetts Institute of Technology Japan Program, in which MIT and Japanese scholars held discussions under the theme, "Meeting a rising China."