An "open and bold" sex festival has kicked off in southern China's Guangzhou city, welcoming teenagers to explore its exhibits.

The four-day event will educate locals about sex culture and sexually transmitted diseases, including Acquired Immuno Deficiency Syndrome, in a bid to "promote sex education and enhance people's sex health," Xinhua news agency said on Sunday.

"The exhibition is open to people under 18, and you will find no warning at the entrance," said Zhang Feng, chairman of the Sex Study Society of Guangdong province.

A similar event held last year had barred entry for the city's very young.

"Knowledge of and access to products, such as condoms, can help minimise possible harm to teenagers who might have sex, as they might be exposed to the threats of venereal diseases and AIDS," Zhang said.