We are getting conflicting reports as to whether we need a visa or not for China.

My wife and I are going on a Celebrity cruise to Asia in 2016. We have two stops in PRC - one for less than one day in Shanghai, and the other in Hong Kong. We will be in Hong Kong for a total of 4 days - two days from the ship and two days on a post cruise stay (part of a travel package). The seller of this package says we need apply entry permit. A person from the ship says we do not need one since 1) we are in Shanghai for less than 24 hours, and 2) Hong Kong does not require it. Which one is correct?