Mmmm...whilst probably an Oriental Reed Warbler, the very short primary projection, apparent lack of streaking on the breast, warm, almost gingery tones above (esp to the crown), supercilium diffuse behind the eye, plus slightly slender looking bill all suggest Clamorous Reed Warbler Acrocephalus stentoreus, which is not on the HK list.
Any more pictures?...
[ Last edited by lpaul at 5/11/2012 11:00 ]