Do I need a visa if I tag on a 5 day stop over in Hong Kong from Guangzhou?

We are flying from Melbourne to London via Guangzhou with China Southern, and would like to add a 5 day break in Hong Kong along the way. Assuming we fly from Guangzhou to Hong Kong on the day we land, returning to Guangzhou and then onto London 5 days later, would we need an entry permit?

One passenger is from UK, one is from Australia.