do german and american citizens need visas to visit Hong Kong/Macau/Kowloon for 4 days?

We would be on a cruise with Celebrity ending in Hong Kong, would stay in HongKong for 4 days to visit Macau and Kowloon before returning to Germany and USA.We are a group of german and american citizens.Which requirement do we need? I was told no visa needed.it's true? Thank you for the clarification!