BEIJING (Reuters) - One woman, a performance artist from Taiwan, tied herself up with bras, but left her nipples exposed. Another artist, a Romanian woman in a bathing suit, had someone write the Chinese characters for "control" and "art" across her buttocks.

But, for the most part, the annual OPEN international performance art festival, held in a secret venue in Beijing out of sight of China's increasingly active censors, was a relatively tame and quiet affair this year.

Only 15 acts performed last month at the long-running festival, which drew an audience of just around 40 people, most of them the artists themselves or event staff.

The reason was a lack of publicity for the two-day event. The organiser, Chen Jin, said he had been concerned about police raids, knowing that the timing of the festival, ahead of a major Communist Party congress, was just too sensitive.

"Performance art is the freest art form. It doesn't have any rules, and this might have scared them the most," Chen said, referring to the authorities.

At its peak in 2009, he said, the festival had an eight-week run with more than 300 Chinese and foreign artists. But it has waned in recent years, mostly due to fears of a backlash from censors.

Last year, the event was forced to cancel halfway through due to repeated police raids, he said.

Performance artists had been in the vanguard of China's art scene as it opened up to Western ideas and values in the 1980s, testing the limits of the law and social norms.

But increased pressure on many forms of art, which comes as President Xi Jinping has been shoring up Communist Party control over all aspects of society, has had a chilling effect on the performance art scene in particular.

In 2014, he urged all artists to "carry forward the banner of socialist core values".

Xi, who is expected to consolidate his power during the congress in October, said artists should "use real-life images to tell people what should be confirmed and applauded, and what must be opposed and denied".

Madeleine O'Dea, author of a new book on dissident artists in modern China, said the country's contemporary art scene was now experiencing a period of retrenchment.

"I definitely feel like things are getting worse and worse," O'Dea said at a book-signing in Beijing last month.

In 2015, an art exhibition on feminism in Beijing was banned. The year before, the 11th Beijing Independent Film Festival was shut down on its opening day.

China's culture ministry declined to comment.

Chen's quiet festival stands in contrast to the Art And China After 1989 exhibition at the Guggenheim Museum in New York City, due to kick off on Oct 6.

The exhibition will feature the works of about 70 artists, most of them born in China, including the dissident artist Ai Weiwei, and delve into what would be considered sensitive topics in China - from civil rights to disillusioned coal miners.

Ai, whose work spans everything from sculpture to architecture, is also known for his performance art - notably the dropping and smashing of an ancient Chinese urn.

Other significant Chinese performance artists in the last two decades include Zhu Yu, whose act featured him biting into a stillborn human baby, and Ma Liuming, whose explicit explorations into sexual identity ran counter to a ban on public nudity.

In contrast, full nudity was noticeably absent at this year's OPEN festival - even behind closed doors.

Beate Linne, 50, a German artist whose work often features nudity, said she stayed covered up because of the timing of the festival.

"It's not nice to the organisers because there might be some consequences," she said.

One aspiring performance artist whose work went viral in July - a dildo placed on top of a flagpole at the art school he was attending - has apparently felt some of those consequence.

The 27-year-old artist, Ge Yulu, lost a job offer at a university because of his act, according to friends who requested anonymity because of the sensitivity of the situation. Ge declined to be interviewed.

His act sparked spirited discussion online about whether it was a tasteless prank, or real art. One veteran performance artist, however, deemed it worthy.

"It was a brave attempt from a young student that came with consequences," said He Yunchang, a 51-year-old Beijing-based artist.

In 2010, He allowed a medical doctor to make a metre-long incision from his neck to his thigh in a performance called One-Metre Democracy in which the majority of the audience voted for the procedure.

He said he was resigned to the government crackdown. When asked if he planned to stage performances in the future, he smiled and said: "I am already dead inside."