"As spot currency weakness and depreciation expectations tend to be self-reinforcing, the People's Bank of China might find it necessary to introduce some circuit breaker, with stronger fixings (the central bank's official daily FX rate) a preemptive move to prevent currency weakness going non-linear," JPMorgan's analysts said in a research note.

The yuan rallied on Tuesday after the central bank set its daily fixing stronger than market expectations for the second day in a row, bolstering speculation that authorities were becoming less tolerant of the currency's weakness.

(Reporting by Marc Jones; Editing by Amanda Cooper)