Hordes descended on the sixth Guangzhou sex culture festival, which opened its doors in Guangzhou on Sunday, paying 30 yuan (about $4.50) to get in. That's triple the fee in 2006.

The annual event, which began in 2003, was free for its first three years. Organizers began charging 10 yuan in 2006, mainly to keep visitor numbers down and children out, according to Zhu Jiaming, deputy chief of the Guangdong Provincial Society of Sexology.

This year's festival features activities ranging from talks on birth control such as condoms to sex toys, a photo show on sexual health and eugenics, forums on sexology, quizzes and lingerie shows.

Ahead of the festival, sexologists gave a series of lectures to middle school and college students, as well as migrant workers. The goal was to improve sexual knowledge and awareness of safe sex, said Zhang Feng, chief of the Guangdong Provincial Commission of Population and Birth Control.

Guangdong, China's largest beneficiary of reform and opening-up and an economic powerhouse, has the most migrant workers in the country, whose numbers are estimated at 30 million.

A six-month survey of 65 such workers found 45 unmarried people aged 18 to 25 had premarital sex. The study also found that the migrants changed sex partners more frequent than local urbanites, said Zheng Lixin, deputy head of the Guangdong Provincial Institute of Birth Control Science and Technology.

"Migrants showed greater tolerance toward sex and were more liberal with sex partners," Zheng said.

Promiscuity among migrants, which had caused sexual and reproduction problems, was endangering the reproductive health of this group of people, warned Zheng, who didn't elaborate.

The festival will close on Tuesday.

Editor: Yan