Hydrophis inornatus

Hydrophis inornatus, the plain sea snake, is a venomous sea snake of the family Elapidae. The Reptile Database lists the South China Sea, with a record from Tsingtau (Qingdao) in China, and further records from Thailand, Java, Sri Lanka and Torres Strait, Australia. (The Reptile Database; Wikipedia, general species account)

It is bluish grey above, with white lips, lower sides and belly. The tail is dark bluish grey with three or four narrow white crossbands. The head is elongate with a somewhat flattened snout, and the dorsal scales are hexagonal with a central keel. (Wikipedia, general species account)