What dialect could this be? (Southern China) I was yesterday in a bus in the HK neighbourhood called 上環/soeng6 waan4. A guy nearby was talking in a strange, almost alien-sounding, Chinese dialect. At some point he mentioned (what I suppose is answering a question) "tseng wan" -- with the "w" being weaker than a normal [w]. I didn't catch the tones but "zeng"/上 sounded much higher than in Canto. I'd guess it's his dialect's version of 上環. It's not Hakka, I think. (上環 in HK's Hakka is song van). According to this site, 上環 is something like sèng vãn in Toisanese. Close but not quite right.

The guy also spoke Standard Cantonese, which is why I suspect it's a Southern dialect.

Any ideas?
I guess it's Teochew (潮汕话 / 潮州话), a southern language in Guangdong and Taiwan. There're actually many Teochew people living in HK. HKers call them Chiuchow people (潮州人). 

You can ask the local friends to know more about them and their language. :)