BEIJING—Investors and companies are increasingly pulling money out of China and its currency in a vote of concern over its growth prospects, a development that could hinder Beijing's efforts to spark a turnaround.

New data published by China's central bank Tuesday showed China's banks were net sellers of 3.8 billion yuan ($597 million) in foreign exchange in July, suggesting that China's exporters aren't converting their dollar earnings into yuan and some investors are taking...