I think flying is the best option. It'll take you ages to arrive at Hanoi
from Hong Kong if you travel by train.

"Doug Pearl" ?????
...
Is it possible to travel by train from Hong Kong to Hanoi? If so, any
idea how long this trip takes? Don't really want to have to stop in
China so I might fly from HK to Hanoi. I'm doing a multi-country trip
and don't want to have to deal with another currency and another visa.

So far I'm going to Japan, Hong Kong, Hanoi... then on to Europe

Thanks,
Doug