Do I need Visa to stay 4 nights in Shanghai ahead of ASIA cruise to Asian countries

I'm living in the US with US passport, and plan to take an ASIA cruise for 14 days thru multiple countries in Asia. The first entry port is Shanghai, then departs to another country in the next 24 hours. However, I Plan to arrive at Pudong International airport in Shanghai 4 days ahead (02/20/2018) of the cruise date (02/25/2018) for sight-seeing in Shanghai. Do I need entry visa if I plan to stay in Shanghai for 4 days ?. Please let me know. Thank you.

Donald Pham