Transit from Flight to cruise with further stop in China

We are flying into Shanghai, for a 2 day stop-over before boarding a cruise ship. The itinerary takes us to Korea, then back to Tanjun, for a 3 day stop in Bejung, before travel to Japan. We understand that the cruise line will take care of our excursion off the ship in Tanjin, but do we need a visa for our time in Shanghai?