China's yuan fell for a third straight day on Thursday to a fresh 4-year low, but traders said the central bank intervened through state-owned banks to limit losses and ease global fears that Beijing may be considering a deeper devaluation. Traders said the central bank appeared to have been caught off guard by the intensity of selling that was sparked off by its surprise 2 percent devaluation on Tuesday, and believe it ordered big state banks to support the currency late on Wednesday. State banks were also believed to be buying on Thursday to stem declines. The spot market closed at 6.3990 per dollar, weakening 0.2 percent from the previous close and has depreciated 3 percent since the central bank devalued the currency.