It turned out to be the event called The ROXY Great Gatsby Charity Ball:-
Official website of the Roxy cinema: http://www.roxycinema.co.nz/
Unfortunately, I couldn't find more photos of Martin at this event last night. Here's one of James Nesbitt though, with The Hobbit's dwarf''s costumes coordinator, Smantha Morley:
Full article: http://www.stuff.co.nz/dominion-post/news/wellington/8800680/Great-Gatsby-ball-fluffs-up-feather-boas
But I did find out that The Hobbit casts were there 2 years ago, at the 1930s themed, The Roxy's grand opening.
Let's wait and see if more photos will surface of Martin... =P