cruise question

I'm a citizen of the United States, flying into Hong Kong for three days. Then I will board a cruise ship that will call for just one overnight in Shanghai, and Shanghai will be the only city visited, and we will leave on the cruise ship with the rest of the other passengers to continue our journey. The itinerary is Ishigaki, Japan — Shanghai — Busan, South Korea. The tours in Shanghai will be booked by the cruise line using government approved tour vendors.

Do I need a visa?