Visa Shanghi. Hongkong

We are arriving from United States on March 1 late evening and boarding Azamara Cruise on March 3.
We will leave the Ship on March 17 in Hong Kong and will stay in that city until Wed. 19 and fly home.
What do we need for application? I have been told that we may obtain a 72 hr free transit permit in both places with out charge? Others have told me that we will have to get them for both places even though they are both in China.