Last updated at 10:17 07 May 2007

It was a sea of flesh almost as far as the eye could see, as 18,000 people stripped off and stood around stark naked.

The hordes bared all for photographer Spencer Tunick's biggest nude project so far.

The US artist's stunt in Mexico City dwarfed his previous record, when 7,000 people stripped off to be photographed in Barcelona.

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Standing up to salute, crouching in fetal positions and lying prone on the tiles of the Zocalo plaza, the volunteers formed a sea of flesh that Tunick snapped from balconies and a small crane in the morning light.

Tunick claimed his work showed the world the human body was something to be celebrated.

"What a moment for the Mexican art scene," he asid.

"I think all eyes are looking south from the United States to Mexico City to see how a country can be free and treat the naked body as art. Not as pornography or as a crime, but with happiness and caring."

The Brooklyn artist has become famous for photographing thousands of naked people in public settings worldwide, from London and Vienna to Buenos Aires and Buffalo.

"I just create shapes and forms with human bodies. It's an abstraction, it's a performance, it's an installation," Tunick said.

"I don't care how many people showed up. All I know is that I filled up my space."

The Zocalo measures 17,500 square metres.

Men and women from a broad cross section of ages and social classes began arriving before dawn, although most volunteers were young men.

"The important thing is not that it's your body or someone else's but that you participate in something as a society," said Oscar Roman Munoz, a 25-year-old engineer. "This reflects the need for change and integration in world trends."

For Tunick's first photo, the models stood upright and gave a military-like salute to their national flag.

In another, they lay down to form a blanket of flesh around a naked man in a wheelchair.

Between shots, they burst out into verses of Mexican folk songs.

Public nudity is hardly a novelty in Mexico City, where protesters often march through the streets wearing only their underwear or nothing at all.