New York City is about 1.4 times smaller than Hong Kong.

Hong Kong is approximately 1,108 sq km, while New York City (including all five boroughs: Manhattan, Brooklyn, Queens, The Bronx, and Staten Island) is approximately 781 sq km, making New York City 70.49% the size of Hong Kong.
Tip: This to-scale comparison of Hong Kong vs. New York City uses the Mercator projection, which distorts the size of regions near the poles.