I've seen a number of these Phylloscopus warblers in an urban park in trees near water in Zhejiang province China. They look evenly pale underneath and, compared to my reference point of willow warblers and chiffchaffs, quite stocky. The photo is not great but hopefully the song will allow ID. There are probably two individuals singing in the recording. Listening to songs online I wondered if it is two-barred warbler.
Michael
Michael