SYDNEY, Australia?Over 5,000 naked people braved a chilly morning to join a mass photo shoot at Sydney's Opera House on Monday, putting a nude twist on the Australian landmark.

People of all ages, shapes, and sizes assembled on the shell-shaped building's steps before dawn for renowned American artist Spencer Tunick, who photographed them with hands raised, lying down, and embracing.

The event, titled "The Base," drew double the expected turnout and was timed to coincide with Sydney's annual Gay and Lesbian Mardi Gras Parade on Saturday.

"Gay men and women lay naked next to their straight neighbors and this delivered a very strong message to the world that Australians embrace a free and equal society," Tunick said.

About half of the 5,200 models were also photographed inside the concert hall.

The artist is well known for his mass-nude art installations, drawing thousands of people to dozens of events all over the world.

"I thought it would be all old people and nudists, but everyone's here. It's great," student Art Rush, 19, told national news agency AAP.

"I'll never get a chance to do this again, it's not worth being inhibited. It doesn't feel sexual, it just feels tribal, a gathering of humanity."

Anna Bruce, 28, said shedding her clothes seemed "really normal."

"It was easier than I expected, it was really normal, there was no problem with getting our kit off," she said.

Scott Faulder, 19, said the installation was "just another excuse to get naked."