It is a finless porpoise. It would be good if you could call 1823 to report the case to AFCD. They would take a record and try to retrieve the carcass.
Below is the details about reporting stranding case. It applies to dead marine mammals found in the sea as well, not just stranded animals.
http://www.afcd.gov.hk/english/c ... n_fin_rep_what.html