Hong Kong is 75% rural montane forests. The city density is closer to 80000/mi^2.

An unsurprising choice, since for a century residents were surrounded by a much poorer, much more dangerous country, and the ocean, in all directions. The only place you can go in Hong Kong to escape are its parks.

Those numbers are the population densities for the whole countries. I wasn't able to find densities for the urban areas of Hong Kong or Singapore.

Btw, Monaco is at 48 462 people per mi2.

Singapore is reasonably dense as a whole for around 5 million people.

If you look at the high numbers for Barcelona, Hamburg or Paris, that's only the urban core. Singapore, of course, also has a denser core.

(And what scythe said about Hong Kong.)