How do I travel to Guangzhou from HK ?Do I need visa?

Hi, at the local East Railway Station, you can catch the direct train to HK. It is very convenient. For the back journey, except the trains between, you can also take the cross-border coaches to GZ. The coaches can be caught at Jordan, Wanchai, Kowloon, Mong Kok Stations or HKIA. Of course, the plane between is also available.

As I know, US citizens can stay in HK for 90 days free visa. Therefore, for your one week stay, a HK visa is not needed. But you have to hold a China visa for mainland visit, dear.