The People's Bank of China set the midpoint rate at 6.4078 per dollar prior to the market's open, weaker than the previous fix of 6.3985, and firmer than Monday's closing quote at 6.4082.
The spot market opened at 6.4130 per dollar and was changing hands at 6.4130 in early trade, 48 pips away from the previous close, hitting its weakest price since Aug. 27.
The offshore yuan was trading at 6.4805 per dollar at its lowest level since Sep. 10, or 1 percent weaker than the onshore spot, the biggest spread between the two markets in the past three months.