State banks are suspected as being the bidders holding USD/CNY, USD/CNH around (ahead of) 6.4
The PBOC has so far gone along with yuan strengthening, but are not keen on a runaway pace of gains. The bidding by State banks rumoured is said to be an intervention effort.
The price has tested towards 6.4 earlier in the session and has bounced, but not by a lot. Offshore yuan chart: