SYDNEY (REUTERS).- Some 5,200 Australians posed naked in front of the Sydney Opera House on Monday for a photo shoot by New York-based artist Spencer Tunick for another signature installation of nudes against urban backdrops.

On a chilly, overcast, first day of autumn, the mass nude photo shoot was titled "Mardi Gras: The Base" and meant to celebrate Sydney's Gay and Lesbian Mardi Gras last weekend.

As the sun rose, Tunick instructed participants to do a number of poses, from standing up, lying down, and even embracing cheek to cheek, for over an hour.

"I want all couples to embrace and kiss, all friends to kiss and all strangers to do whatever they want," Tunick said as he directed the crowd.

Some participants were surprised at how asexual, and leveling, the event was.

"I thought it could be a bit awkward, but it's funny because when you're naked and everybody else is naked, you feel like you're dressed, because everybody looks the same," said Steven Anglier, who wore a wig so he could stand out in the photo.

"It's really a weird experience because you think there could be something sexual behind, but there's not."

Tunick has produced almost 100 installations around the world, and says his work is not about exhibitionism or eroticism but instead reveals the vulnerability of life in a rough city landscape.

But that argument has not impressed authorities at home in the United States, where Tunick has been arrested seven times.

His largest installation was in Mexico on May 6, 2007, where he photographed 18,000 people In Mexico city's Zocalo Square. (Reporting by Michael Perry; Editing by Miral Fahmy)