Northern Vietnam : Dong Dang
Once you cross the border from Pingxiang to Vietnam, there are several taxis waiting for you. Price should be around $5 and takes about 15 min to Dong Dang. Taxi will probably take you to some private minibus company which will offer you transportation to Hanoi. Initially, they will ask $10/person, but don't pay more that $5/person. The trip to Hanoi takes a few hours.