A senior Hong Kong cultural official said on Thursday that freedom of expression was not above a China-imposed national security law, on the eve of the opening of a contemporary art museum intended to put the city on the global cultural map.

The multi-billion dollar M+, featuring contemporary artwork from leading Chinese, Asian and Western artists is Hong Kong's bid to match museums like the Tate Modern in London, the MoMA in New York and the Center Pompidou in Paris.

But the imposition of a sweeping national security law by China last year on its once freest city is casting a pall over the opening, as curators and artists struggle to find a balance between artistic expression and political censorship.