China's yuan posted its biggest daily gain in seven months on Thursday, closing 0.3 percent firmer at 6.1976 per dollar after the central bank strengthened its guidance rate. The People's Bank of China set the midpoint rate at 6.1213 per dollar prior to market open, firmer than the previous fix 6.1247. The spot market opened at 6.2185 per dollar and closed 1.25 percent away from the midpoint. The spot rate is currently allowed to trade with a range 2 percent above or below the official fixing on any given day.