Over 5,000 people stripped off all their clothes outside Sydney Opera House as part of photographer Spencer Tunick's latest art project.

Tunick is famous for his installations which involve large numbers of naked people pictured in urban locations.

The work, commissioned by Sydney Gay and Lesbian Mardi Gras, was called "Mardi Gras: The Base".

Mr Tunick said that it had been difficult to persuade the straight people to embrace the gay participants, but he succeeded in the end.