The onshore yuan fell as much as 0.6 percent to 7.3084 per dollar, its weakest level since December 2007 and close to the lower limit of the trading band set by the central bank on Tuesday.
The yen fluctuated against the dollar as speculation swirled that Japanese authorities had stepped into forex markets again to support their currency for a second time in as many sessions.
Forex traders were also keeping tabs on the yen as it edges closer to 150 per dollar, with Japanese officials holding off a second intervention in as many months but saying they are ready to act when necessary.