Visa required for ship cruise stop at Shanghai?

Hi, I'm from Malaysia and would be going on a ship cruise next month, boarding from Busan, South Korea. The ship would stop at Shanghai for a few hours where we can opt to get down for a short sightseeing.

Since we would be stopping for several hours only before leaving back to Busan the same night
I read about the 72-hours free transit but it seems applicable for those travelling by air. How about us that would be travelling by sea?
Pls advise.

Thanks.