ajohn

Some juvenile Oriental Reed Warblers can be seen in HK in September and tend to look rather worn and scruffy. The iris on your bird looks dark grey, which is characteristic of birds in their first year, but the feathers look fairly fresh and it has presumably moulted out of juvenile plumage (I think all have moulted by this time of year). So, I think this is a first-winter Oriental Reed Warbler.

Congratulations on your tick!