Bitcoin plunged by as much as 12 percent on Friday after China's central bank urged investors to take a rational and cautious approach to investing in the digital currency, which is on track for its heaviest two-day drop in two years. It continued that fall on Friday, with its losses accelerating after the central bank's warning. The Shanghai head office of the People's Bank of China (PBOC) noted in a statement that bitcoin prices had shown abnormal fluctuations in recent days, and said those investing in it should do so carefully, with awareness of the currency's volatility.