Ok, this is Oreocryptophis porphyracea nigrofasciata. Yep, is quite a mouthful. And one reason why I do not often use latin names.
Its common name is the red mountain racer, but as a friend pointed out a much more appropriate name would be the orange slope crawler, as that is a far more accurate description.
Not such a common snake in Hong Kong, maybe because they are often found at dawn or dusk, not typical hiking times.
more information on this and lots - in fact all - of the otehr snakes of Hong Kong can be found at our sister site www.hongkongsnakeid.com
information from that site:
Varies in color from light brown to salmon to red to peach, usually reddish when not about to shed its skin, brown when shedding. Small red and black eyes on a long thin head rounded at the nose. Body color uniform from head to tail. Two black stripes running from the eyes down the length of the body along either side of the spine, sometimes faded, often intact. Additional short black stripe runs lengthwise from the nose to the back of the head.