Hmmm. An interesting bird. The head pattern and small black breast patch possibly favour
leucopsis. But the paleness of the back and lesser coverts, and the dark centres to median and greater coverts favour
baicalensis. It's difficult to judge the extent of black in the rump/lower back which may help decide on ID.
I suggest you submit the photos to the Records Committee on an Unusual Record Form (
http://www.hkbws.org.hk/web/chi/ ... ies_report_form.doc).