Transit visa for Shanghai for an Austrian Citizen

Hello, I am currently in Tokyo and would like to spend three days in Shanghai before travelling to Hong Kong. I inquired at the Beijing airport if I could do this by applying for a 144 hours transit visa, once I am at the airport in Shanghai. I was told by the immigration police that this was OK, as Hong Kong has a special status. Could you please confirm this to me ? Many thanks and best regards from Tokyo!