China's recent clampdown on foreign media is crimping the expansion plans of Western news organizations, at a time when many experts believe the Chinese market for news and financial data could be poised for explosive growth.

Among the news- and financial-information providers whose Chinese or English-language sites have been blocked inside China in recent months are Bloomberg LP, Thomson Reuters, the New York Times and The Wall Street Journal. Meanwhile, dozens of China-based Western journalists have been told their annual...