Hong Kong to Shanghai - Shanghai to Hong Kong - 72 hour free transit allowed?

Hello,
We are 2 people flying from Denmark (UK passport and a Danish passport) to Singapore then to Hong Kong. We want to go for 2 nights to Shanghai from Hong Kong and then back to Hong Kong. Do we need to get a visa for this or are we able to take the 72 hour free transit allowance for the Shanghai/China part?

Hong Kong - Shanghai (2 nights)
Shanghai - Hong Kong (returning several days later back to Denmark).
Many thanks,
Mel